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Hey guys, Looking at getting a 6.6 gasser. 2020-2023 offer the 6L90 and 2024-2025 have the "Allison" but not Allison 10 speed. I don't have to have the latest and greatest or the fastest, just want something reliable. I had a 1500 with the 6L80 and had the typical converter issues around 100k miles. Do not want to see anything like that in the 6L90. The 10 speeds seem to have their quirks, and aren't even a true Allison, which is a disappointment. Basically, a 6 speed that has been around for years (6L90) or a newer updated trans that has not been out long enough to show reliability (10L1000). Thoughts?

Hello all, I'm going to be adding the transmission oil cooler (GM Part Number 23409058) to my 2020 Trail Boss. I’m going to order the ACDelco Oil cooler lines (GM Part Number 86560008). Does anyone have any detailed photos of how the lines are run under the body, through the engine compartment, and out of the core support to their cooler? Any help is greatly appreciated. Thank you so much!

As everyone here already knows…”it shouldn’t take more than a few minutes” turned into me pondering how many fist sized dents I needed in my door panel for aerodynamic efficiency or the “golf ball” look. Anywho. I delved into the underside of my custom trail boss in an attempt to install a dipstick in my 6L80. Of course, I must mention that the 6L80 was present in the 4.3 models until at least the 2020 model year (RPO code MYC), this dipstick fits all 6L80/90 transmissions as far as I’m aware, in the 6/8 cylinder engines alike. Here is the order of operations. NOTE: TRANSMISSION CROSSMEMBER REMOVAL OR DROPPING THE REAR OF THE TRANSMISSION WAS NOT REQUIRED. FOR MY APPLICATION. Remove dipstick from tube to make installation easier. The dipstick gets in the way otherwise. Also, lube the seal and tube with white lithium grease to ease insertion. In order to access the hole where the plug is (that must be removed prior to installation), there is a heat shield that needs removal on the passenger side of the transmission. It is held on by two 10 mm bolts. Beware of the front one, it’s blocked by the bend in the shield, and too close to the catalytic converter to get a regular 3/8” ratchet and shallow well socket in there. After removing the heat shield, you can use a trim tool, your fingers, or a screwdriver to remove the plug where the dipstick enters the transmission (there is only one location it will go). Then, find the studs on the backside of the bellhousing, and locate the one below the starter hump. Using a 15 mm deep well, swivel, and breaker bar or 1/2” ratchet, remove the stud. Test fit and place it in its approximate location, but beware the ground strap on the back of the block, right next to the path of the tube, there is a chance it gets in the way like mine, and you’ll need to loosen it in order to route the tube unabated. 15mm bolt. Install your dipstick seal first, you can use a thin layer of white lithium grease for ease of insertion. Follow up by seating the tube in the grommet, and then reinstall your bell housing stud. Be mindful that torquing that stud could cause the dipstick to raise out of the hole, so it’s wise to keep light pressure downwards on the tube to ensure it stays in the transmission until you snug and tighten the stud. Once the tube is seated and the stud installed, make sure your O2 sensor wire holder/zip tie is still in its pocket on the transmission, and reinstall the heat shield. If you had to loosen or remove the ground strap on the block, reinstall/tighten the bolt. Use the procedure sent with the dipstick to check level and add fluid as needed. Mine needed 1 quart (this is typical, mine didn’t leak and hasn’t lost fluid.). This dipstick does work with aftermarket and deep pans. Lubelocker also makes a reusable gasket for the 6L80 and one for the 6L90 if anyone is interested.

Hello all. I am a semi-frequent user of GMTrucks.com. I’ve had several cosmetic and suspension modifications to my truck (Bilstein 5100’s, roadactive suspension, hellwig rear sway bar, interior mods), nothing major in the drivetrain. I just crossed 50,000 miles, and it looks like yet another TCC failure (first one at 24,500 to 25,000 miles). It’s a 2020 Custom Trail Boss, 4.3. When the first converter failed, they ended up putting 2 thermal bypass valves in it. After the last TBV change, transmission never sees over 150°. What do I need to do to have GM put a better converter in my truck to prevent future hangups (sonnax, maybe)? How should I approach this to ensure I don’t keep losing my truck for weeks at a time? I don’t overload it, I don’t dog it, and the fluid still looks clean (changed with last thermal bypass valve at 30,000 miles, total fluid exchange and filter replacement). It seems like every 25,000 miles, I’ll be back for another torque converter. I don’t haul or tow frequently. When I do, it’s usually no more than a single axle utility trailer with some light household refuse, or an enclosed single wheel with a flat track motorcycle in it. Bike weighs 600 pounds. Tongue weight below the 1,760 payload rating on the sticker in the door. I’ve never gone more than about 40 miles when towing. Usually interstate or rural rustic road (55 mph and no traffic) Any suggestions? I really like the truck and don’t want to trade it in. It suits me for what I need, and I’ve put a lot of time and love into this machine.

Just finished a Top end on my 6.0 at 191k and made a run to South Dakota dropping off a FWC camper. Loaded my 4K lb. truck camper, making a run to Oregon for a new client opportunity. 40 miles from home felt a slight resonance in the steering wheel while rolling onto an overpass. RPMs at 1800, in 5 gear noted a slight increase in rpm (50) when resonance cycled every 30-40 seconds. Switched manual gear selection to 4th showing 3000 rpms and resonance stopped. Knowing the climbs ahead, 81 miles out, turned around and headed home. Took the truck to the shop, gave a detail report. Shop confirmed my observations and pulled the pan. I’ll update the site and detail the repair. 15k miles on third transmission filter change. Pan showing metal bits and magnet covered as well. Shop suspects a torque converter fail.