2012 Tahoe Strange Drivetrain issue. Traveling; need Help!

[TerryKing]

Hi Everyone,

Traveling Vermont to Florida; now at Asheville NC. Towing small 20' camper.

Yesterday we started to get a strange symptom:

- Every 2 to 4 seconds approx. the RPM drops a little, then jumps back up. Only 100 to 200 rpm change.
- Happens in all gears; more noticeable under load in 5th and 4th. I usually run 5th with the camper.
- There is a noticeable jerk when the rpm jumps back up.
- Occasionally might get a short shudder?
- Engine power/mileage seem pretty normal.
- Problem started just after filling tank with non-main-brand gas but 2 tanks now of good fuel; one with higher octane. Not getting any better.

First noticed with cruise control level ground.. suddenly didn't hold speed. Running manually since.

Worried; and brought truck to Asheville Chevrolet dealer; they ran all their tests: no codes, no history of codes. Transmission fluid looks good; level normal. Transmission temperatures normal for me: 170 or so on highway, and 205 going up up hill over Rt 26 mountain. Added some fuel conditioner stuff on GM dealer suggestion.

I need your opinion on what is happening here. I'm about to go out on the road headed South. I don't expect it to have fixed itself overnight.

So ?? ??? ? Transmission? Other running gear?

What have you ever heard of similar to this? What should I do / look for?

Love this truck!

THANKS!

Regards, Terry King ...From the Woods In Vermont terry at terry king dot us\
(I can monitor here on the road)

 

[davidzog]

Can I ask how long ago it had new spark plugs and wires??? Sounds like an intermittent plug miss, but not enough to set a code. Had this happen before....hope that helps.

 

[gpracer1]

Sounds like a torque converter slipping or getting kicked off by misfires.
When my 99 had misfires detected it would disable the TC lockup for a bit.

 

[adventurenali92]

When I had my spark plugs changed over ther summer it did a similar thing. Very small rpm changes. I didn’t get a noticeable jerk although you could feel it skip a beat sorta and then regain itself. My #8 spark plug, which is the hardest to get to, the one all the way at the back of block on the passenger side just about up against the firewall wasn’t seated all the way. Took it out and reinstalled and correctly seated it into its position. That fixed the issue.

 

[SnowDrifter]

Can you hear/feel a misfire?

If not that, then it sounds like a torque converter lockup issue

 

[TerryKing]

Hi guys, thanks and I'm still trying to figure this out while still driving to my destination.

Not an obvious misfire; no CEL
The rpm slowly drops over 4..5 seconds then jumps up. Feel a little bump at that time.

Worst in 5th under load. I am actively downshifting to 4th for a little, then back to 6th which will run more smoothly on the level. Not good but surviving.

This is an electically controlled transmission, right? Lots of sensors and solenoids? I need to find a good GM dealer in northern Florida with a good transmission person. This has to get fixed. Once we get in a destination campground I can have the truck in the shop for a little while..

Any suggestions welcome!

THANKS!

Terry ...OnTheRoad

 

[thompsoj22]

once you get to destination and drop the trailer take it out and see if the issue duplicates without the load? A trans is just as hard to troubleshoot as electrical when it's intermittent. If it will glitch for the shop with a test drive they may be able to narrow it down. This is the 4L80/6.2 correct? Also if the vehicle get's your family safely to the campground than it's a good truck and worthy of whatever the cost is to repair. If it craps on the freeway, tow it to the dealer and trade it in on a different one, if your towing with the 5.3 4L60 you are absolutely underpowered/wheelbased to tow anything other than a 4x8 uhaul trailer. we also tow a travel trailer and traded our 03 tahoe in on our 08 denali xl1500 6.2 and never looked back. if you love your tahoe you will feel the same about the denali. RV'ing is one of the most expensive/fun ways of traveling, If you love the trailer and it works for your family than buy a different tow vehicle in florida.

 

[TerryKing]

THANKS for the information and ideas..

We are at a campground near Sarasota. We'll be in another one for 5 days starting Monday. Two GM dealers nearby are Sunset Chev-Buick-GM in Sarasota and Starling Buick GMC and Bill Buck Chevrolet. Does anyone have any experience with any of these??

THANKS...

 

[TerryKing]

OK, going into dealer tomorrow.

Question: Is "Shudder" always a torque converter symptom? What else could cause it?

Thanks!