Looking to Buy '18-'19 Tahoe Engine/Trans questions

[Plimbob]

I have a 87 diablo tune on my 18 with 6 speed and 5.3. I may do a Lew tune this summer, but just switchihg to the firm shift, cutting the afm, and increasing throttle response 20% makes it a completely different vehicle, though I also have a airaid jr and corsa exhaust. I like being able to pull the tune if I need to go to dealer, though I have not needed to yet. I had considered a whipple, but really dont feel underpowered any more, nor do I want to buy premium gas...

I have an air raid Jr on mine as well but no other mods. Not sure the Airraid does much other make it sound better. I will say the rebuild on the trans made a further difference in firmness in shifting.

Regarding the trans it operated fine one day and then started dropping into neutral occasionally and then got worse over a 3-4 day period.

 

[Timbers68]

The 6 speed trans is tunable. The 10 speed is not with the factory TCM - you need to add/swap or replace in module in order to tune the trans (Google House of Power T93 or T97 - I don't remember I'm going off recall.) The 10 speed is a very good trans but as stated by @lbenson there aren't enough high mileage examples.

The 6 speed can be made bullet proof with cheap dollar mods. Change the fluid and filter every 25k - forget what GM tells you. The next biggest thing it having the thermostatic valve pulled from the trans so it just flows the trans fluid without any restriction. It sits in the outflow of the trans lines. Pull the lines and remove the valve. If you want an upgrade, replace the lines - The trans lines were upgraded. Trans temps will drop from 185 to 140 for normal driving. With the trans lines/valve, fresh fluid, and the tune, trans should easily hit 100k even with towing.

This might be overkill for your situation but the next big leap is an aftermarket torque converter. Its bigger dollar but a lot of the trans issues stem from the crappy factory converter. Get a big brand name like Circle D, TCI, Yank, etc.

And I've got 3.08s out back in the Suburban.

Let me know if you need more questions answered.

Thanks for this info.

 

[Timbers68]

FWIW -

I have a 2017 Tahoe 5.3L with 90k so I can't opine on the 6.2L. I have had issues with the AC Condenser, the brake booster and the 6 speed failed at 87k. When I had the 6 speed rebuilt, I have them put in a Billet TQ, Sonnax valves and upgraded thermostat. The trans shift better and considerably firmer, however, it does downshift pretty ******* de-acceleration into 3rd so I need to look at that further. BTW - the shop who rebuilt the trans said they do 6-8 of the 6 speeds a month. Obviously, a serious problem.

I have tuned it with the Diablo tuner and custom tune by Lew Eaton. It runs and tows better. I tow a 20 ft fishing boat around the Midwest and it tows pretty well.

I am getting some of the vibration issues at 65-75 mph as some others have complained about. I have checked the tires, tie-rod and ball joints not issues there. So still working on this issue.

Thanks for your reply and info.

 

[Timbers68]

I have a 87 diablo tune on my 18 with 6 speed and 5.3. I may do a Lew tune this summer, but just switchihg to the firm shift, cutting the afm, and increasing throttle response 20% makes it a completely different vehicle, though I also have a airaid jr and corsa exhaust. I like being able to pull the tune if I need to go to dealer, though I have not needed to yet. I had considered a whipple, but really dont feel underpowered any more, nor do I want to buy premium gas...

Good to know on not feeling underpowered.

 

[Kcryzac]

The 6 speed trans is tunable. The 10 speed is not with the factory TCM - you need to add/swap or replace in module in order to tune the trans (Google House of Power T93 or T97 - I don't remember I'm going off recall.) The 10 speed is a very good trans but as stated by @lbenson there aren't enough high mileage examples.

The 6 speed can be made bullet proof with cheap dollar mods. Change the fluid and filter every 25k - forget what GM tells you. The next biggest thing it having the thermostatic valve pulled from the trans so it just flows the trans fluid without any restriction. It sits in the outflow of the trans lines. Pull the lines and remove the valve. If you want an upgrade, replace the lines - The trans lines were upgraded. Trans temps will drop from 185 to 140 for normal driving. With the trans lines/valve, fresh fluid, and the tune, trans should easily hit 100k even with towing.

This might be overkill for your situation but the next big leap is an aftermarket torque converter. Its bigger dollar but a lot of the trans issues stem from the crappy factory converter. Get a big brand name like Circle D, TCI, Yank, etc.

And I've got 3.08s out back in the Suburban.

Let me know if you need more questions answered.

We’re is the thermostatic valve? near the radiator ?

 

[fozzi58]

We’re is the thermostatic valve? near the radiator ?

Right inside the tube of the trans lines lines. I believe its the inlet side.