2011 2500hd 4x4 6L90 shifting issue

casey.mikl · March 29, 2019

I have a 2011 Silverado 2500hd 6.0 4x4 with 6L90 transmission. Truck has 102k miles on it. Within the last 50 miles the truck has developed a shifting issue. The truck was dyno tuned prior to my owning of it. 1st to 2nd shift has always been firm and the occasional firm shift into 3rd. It has started to slip when going into reverse and into drive. When the fluid is cold, it shifts and works fine. When it’s warm, it shifts weird and when going into reverse or drive, there is a delay and it will not go into gear unless you bring the rpm up to about 1500-1700 rpm. While driving, 2-3 and on shifts feel like you let off the gas for a short period and then it bangs into next gear causing the truck to jerk. It has a few times downshifted when I got into the gas and the rpm went up but the truck did not gain any speed. I have owned it for the last 20k miles and I have not changed the trans fluid or filter. The fluid is dark, but not burnt or does not smell. Tomorrow I am planning to change the fluid (3 gallons, going to use 2 jugs and attach hoses to cooler lines so that it sucks new fluid in and spits out the old fluid) and change the trans filter. I did add 1 pint of sea foam trans tune into the trans and took it for about a 7 mile ride, making sure it shifted though all the gears various times to work the fluid through the trans. Since the trans has started to act up, I have stopped driving it to avoid damage to the transmission. I believe it possibly has a torque converter issue, as the gears don’t feel as if they are slipping. I’m really hoping it’s a fluid issue and new fluid and filter will fix it. When I had the snapon scanner hooked to it, it did say ATF life 9%. Would anyone be able to shed some light on this maybe and be able to help me out? I’m also looking at changing the transfer case fluid as well while I’m at it.

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casey.mikl · March 30, 2019

Changed filter and got out about 8 quarts or so of trans fluid. Refilled it and took it for a drive. Still shifts like it did. At about 55mph I got a loud screeching sound like metal to metal. Got that a couple of times. And I brake torqued it in the drive way and something slipped and got a big smoke show. So looks like it will be going away for a new transmission.

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