MrEvanchi

Had something similar, ended up being the center differential carrier bearings. Of course that'd be wheel speed dependent like yours. The whole tail-section of the transmission pops off which is where the countershaft, center differential, and all their bearings live. Not too difficult, it's just glued on with RTV which is tough to pop off. (There was a good writeup on the forum I referenced long ago when I did mine, including all part numbers.) ( Alternatively, those aren't the only bearings it could be. There's a solid chance your front differential bearings are the cause too, which would make much more sense if your mechanic very confidently narrowed it down the front, and not the rear of the transmission. Mine manifested much like a whirring/whining noise, and only got worse and louder as I continued to drive it.

I haven't come across any AFR compensations in my 07 LGT's stock ROM, but it does at least pull timing with extreme coolant and IAT temps. -2.11* @ 212F, -3.87* @ 230F Coolant And -2.11* @104F-158F, -5.98* @176F+ IAT

Just realized there was even a thread here devoted to gaining Flex Fuel support. Boy what an emotional roller coaster of a read this has been. I'm stoked! Been dying to have flex fuel on my 07 LGT since forever. I'm getting giddy at the thought of it finally becoming reality! Emailed Cobb about my interest, and asked for any new ETA's. I've certainly got cash quarantined for this.