2016 Yukon/L680 Transmission upgrades for HD TOW 2016 Yukon XL

Hi all,

I just purchased a used 2016 Yukon with 40k miles and HD tow package to be able to pull an 7500 GVWR RV trailer.
Due to all the "transmission failure" complaints here, I am worried about the transmission reliability on long trips and if it would be a good idea to upgrade the torque converter, or any specific components for heavy duty tow applications to avoid a catastrophic failure that would require a whole transmission swap.

I've weighed in to ensure it's well below the GVWR of the tow vehicle axles etc. It has no issues towing and performs very well.
I've also installed a Mishimoto transmission oil cooler and performed the Thermal Bypass Valve SB below and the transmission oil never goes above 190F even towing long distances or in stop and go traffic.

Here are some Performance Upgrades that look promising, but I don't know what I'm looking at. If anyone can advise on exactly what parts are known to fail and the best cost benefit or best preventative measure would be, if any at all, please advise.


Upgrades performed thus far:
1. Cooler valve Thermal Bypass Valve service bulletin
Service Bulletin INFORMATION
w/ part number 86774933

2. Mishimoto Transmission Oil Cooler:
MMTC-K2-14

3. Range Technologies AFM disabler


Thanks in advance!

Welcome from NYC!

Welcome to the Forum.

Does your Yukon have the "NHT" option code for the Max Trailering Package and "GU6" for the 3.42 rear axle ratio on the sticker in the glove box? Without NHT and GU6, the maximum combined vehicle and trailer weight is 2000 pounds less. It's in the fine print in the owmer's manual. The weight of passengers and cargo in the Tahoe are supposed to be subtracted from my max trailer weight. Again, It's in the fine print in the towing section of my Tahoe Owner's Manual.

This thread has a bunch of info on towing.

I'm with you on the concern about towing or even driving a higher mileage Tahoe with the original transmission and torque converter. I thought I was set with my Max Trailering package towing a 3,300 pound trailer. Then my Torque Converter Clutch (TCC) started slipping and coming apart on a trip when I wasn't towing.

I've always tried to anticipate up shifts and back off on the gas pedal so the shifts would not be under load to make it easier on the transmission.

It's good that you have the SB thermal bypass valve and AFM delete. You might need a larger auxiliary transmission fluid cooler if you're seeing temperatures as high as 190°F.

Your vehicle has lower mileage so the transmission may have more life left in it. But when towing 7,500 pounds you are putting a lot of torque through your transmission.

I hear you on having a trip interrupted. You can see my experience here
and suggestions received for transmission upgrades.

I understand that the torque converter is the weakest link and when the lockup clutch goes it contaminates and takes out other sections of the transmission with heat being the initiating cause of the TCC failure. I cruised at 60 mph in Tow/Haul mode in fifth gear and typically cruise at 65 in sixth gear when not towing.

I have towed over 10,000 foot passes in the Rockies four times that I can think of. When towing uphill I downshift and don't go over 3,000 RPM. I do my best to drive in a manner to get best miles per engine and transmission rather than driving for max performance. At higher elevations the ambient air pressure is lower so that becomes a limiting factor in developing power which keeps the engine from working as hard as it can closer to sea level.

I have a ScanGaugeII

which shows up to four parameters from the vehicle databus. It can also scan for trouble codes.
I can see engine parameters like the Manifold Air Pressure/Manifold Absolute Pressure (MAP). That is the pressure in the intake manifold pushing air into the cylinders when the intake valves are open. I try to keep it below 13 psi (about 26 inches of Hg [mercury]). I usually also display digital engine temperature, digital alternator voltage to the tenth of a volt, and RPM.

For what it's worth, the Scan Guage Intake Air Temp shows that my Tahoe already has an effective cold air intake system. Same on two other OBDII vehicles on which I have used it. Factory engineers aren't dumb. Cars and trucks have had cold air intake systems since the mid 1970's. An aftermarket cold air intake may make more noise, but not more power.

If you haven't done it, you might consider dropping the pan to see what debris might be in it or the filter and then do an annual flush of the transmission fluid as long as you are towing. You may already know that dropping the pan and refilling the drained fluid only replaces about 40-50% of the fluid.

Wishing you the best. Rob

Thanks for the response and warm welcome! I did see your post and could not sleep for a few nights....and didn't want to jack your thread, so I thought I'd start another thread on preventative measures. @NickTransmissions had some very valuable information in there about what you should expect in your rebuild. I've seen some other references to upgraded hydraulic pump, and deeper trans oil pan, so in light of that I'm wondering what should be done in advance for the 6L80.

The trailer actually weighs only 5100lbs empty and I try not to load it up, I believe the max weight rating is the 7500. I've done the CAT scale weight and done the online tow calculator to ensure the axles and combined vehicle weight aren't over their Gross weight rating.

What is the target trans oil temperature range? I couldn't find anything on bobistheoilguy about this.The aftermarket cooler holds about a quart of fluid, I've attached a picture for size reference. Should I install a deeper trans oil pan? Would that help lower the temperature due to higher fluid volume?

See attached, I see the part numbers you referenced on the sticker.

@RobH thanks for the Scan Gauge tip. That looks promising, and cool! My problem is that I use the OBD port for the Range AFM disabler, so maybe I need to do the delete instead so I can get a Scan Gauge.

With a "tune", you can disable the AFM electronically in the Engine Control Module/computer (ECM). Basically, the ECM reads a parameter/settings file when the ignition is turned on. The file tells the ECM how to manage the engine. A tuner program reads the ECM settings file, edits it, and then writes the edited file back to the ECM. You may already know this.

You may already know that you can go to a GM dealership parts counter with your VIN and get a printout of your vehicle's build/option codes with a plain text description of what each code means.

NiamLeeSin said:

I've seen some other references to upgraded hydraulic pump, and deeper trans oil pan, so in light of that I'm wondering what should be done in advance for the 6L80.

Click to expand...

Welcome to the forum, @NiamLeeSin!

Short answer to your question: Do as much as you can for your 6L80 that squeeze into your budget.

Simple performance list:
- Sonnax Zip Kit + Clutch Boost Valve ream/OS CB valves (all three) if those valves are bad + new check balls (your transmission will have 8 check balls, not 7)
- Overhaul pump completely (machine working surfaces; set rotor and slide to working deck surface .002" clearance) new rotor/slide, Transgo unbreakable pump ring kit); replace stator if there's any wear on journal surfaces/bore, etc
- New Bushings everywhere
- Reinforce welds on 3-5-R drum (2016 doesn't have nearly the extent of failures here but better to be safe than sorry)
- Sonnax billet 4-5-6 clutch hub
- Sonnax 4-5-6 clutch piston kit (gives you an additional friction and steel plate)
- Borg Warner High Energy friction module - all clutch packs
- Deep pan
- Biggest, highest capacity aftermarket transmission cooler you can fit on your vehicle (done) - keep trans temps around 160-180 max)
- Cooler bypass valve delete or update (done)
- Torque Converter w/billet cover and .070" thick converter clutch (or triple disc set up - Circle D, TCI, FTC are a few reputable converter builders)
- Heavy Duty GM/AC Delco parking rod to prevent failure there
- Rear planetary carrier w/billet drive plate
- Good tune for towing (6L80Es benefit from tuning more so than previous transmission families, IMO) - check out Black Bear...lots of folks on here use them and have good things to say from what I've seen.
- Replace TEHCM, IMS and harness/speed sensors w/new ones from dealer (costly but worth it) - bring your TEHCM part number and vin so they can provide correct parts. Check your new rear speed sensor against your old one to make sure it's the same (2012+ rear speed sensors changed to coincide w/transition to uni-gear ring gear design).

Hope that helps!

NickTransmissions said:

Welcome to the forum, @NiamLeeSin!

Short answer to your question: Do as much as you can for your 6L80 that squeeze into your budget.

Simple performance list:
- Sonnax Zip Kit + Clutch Boost Valve ream/OS CB valves (all three) if those valves are bad + new check balls (your transmission will have 8 check balls, not 7)
- Overhaul pump completely (machine working surfaces; set rotor and slide to working deck surface .002" clearance) new rotor/slide, Transgo unbreakable pump ring kit); replace stator if there's any wear on journal surfaces/bore, etc
- New Bushings everywhere
- Reinforce welds on 3-5-R drum (2016 doesn't have nearly the extent of failures here but better to be safe than sorry)
- Sonnax billet 4-5-6 clutch hub
- Sonnax 4-5-6 clutch piston kit (gives you an additional friction and steel plate)
- Borg Warner High Energy friction module - all clutch packs
- Deep pan
- Biggest, highest capacity aftermarket transmission cooler you can fit on your vehicle (done) - keep trans temps around 160-180 max)
- Cooler bypass valve delete or update (done)
- Torque Converter w/billet cover and .070" thick converter clutch (or triple disc set up - Circle D, TCI, FTC are a few reputable converter builders)
- Heavy Duty GM/AC Delco parking rod to prevent failure there
- Rear planetary carrier w/billet drive plate
- Good tune for towing (6L80Es benefit from tuning more so than previous transmission families, IMO) - check out Black Bear...lots of folks on here use them and have good things to say from what I've seen.
- Replace TEHCM, IMS and harness/speed sensors w/new ones from dealer (costly but worth it) - bring your TEHCM part number and vin so they can provide correct parts. Check your new rear speed sensor against your old one to make sure it's the same (2012+ rear speed sensors changed to coincide w/transition to uni-gear ring gear design).

Hope that helps!

Click to expand...

Thanks for the info. My gut tells me these items require rebuilding or dismantling the transmission to a high extent. Does it make sense to do all of that now, or just wait until it fails? I will do deep pan with plug, but are any of these items within that level of complexity/cost? Which would you say are the low-hanging fruit?

NiamLeeSin said:

Thanks for the info. My gut tells me these items require rebuilding or dismantling the transmission to a high extent. Does it make sense to do all of that now, or just wait until it fails? I will do deep pan with plug, but are any of these items within that level of complexity/cost? Which would you say are the low-hanging fruit?

Click to expand...

Sorry, thought you were going to rebuild the unit (if that was the case, everything's low hanging).

For minimally invasive internal work:
- Sonnax zip kit
- Tehcm refresh kit
- new spacer plate and check balls (cbs come in the Sonnax kit)
- deep aluminum pan
- new filter (cut open your old one to see if any metal or chunky clutch material has passed through it
- tune from someone who knows what their doing

Between this shorter list and what you've done already, Id leave it alone unless you're having issues. Save the rest of the upgrades for when you go through the unit.

NickTransmissions said:

Sorry, thought you were going to rebuild the unit (if that was the case, everything's low hanging).

For minimally invasive internal work:
- Sonnax zip kit
- Tehcm refresh kit
- new spacer plate and check balls (cbs come in the Sonnax kit)
- deep aluminum pan
- new filter (cut open your old one to see if any metal or chunky clutch material has passed through it
- tune from someone who knows what their doing

Between this shorter list and what you've done already, Id leave it alone unless you're having issues. Save the rest of the upgrades for when you go through the unit.

Click to expand...

Perfect thanks!