If its a certain rpm, my guess is that its not engine related, but transmission related. Mine started that way, then at other rpms based on gear shifts. Much worse uphill than downhill acceleration. In the space of 3 days it went from noticeable to undriveable. No codes were thrown until the car couldn't move and the tcm disengaged the transmission. All this happened when I was at the highest elevation road in the Angeles Forest, truly the middle of nowhere when it comes to SoCal.
2 weeks later, I get my car back from dealer a couple days ago. Drives like new.
$5,526 transmission replacement with 100,000mi unlimited time warranty.
My odometer was at 100,700 when it happened. Didn't faze me, expected it when I first bought the car new (2015 Denali awd). Wouldn't have bought it if I couldn't get the max extended warranty at dealer cost ($3,750 for 150,000mi 6 yrs)
Triple drain/refill at 49k mi and 97k mi, didn't make any difference. 1-3-5-R waveplate, some solenoid, chunks of metal in the fluid. Oh, I had added a temp-controlled fan equipped high performance transmission cooler when I first bought the car. Fluid was always kept on the cool side. Didn't help either. Master tech said I did everything right. My interpretation of that was that nothing can be done to prevent premature failure of a poorly designed transmission. It is what it is.
Now that the GX460 is avail with captains chairs (2017+), I know what will be next for me.
Last edited by psychoknightx; 04-19-2019 at 12:19 AM.