K so here's my problem: (by the way transmissions are my least favorite area to work on) My 07 Sierra started doing this roughly 3 months after I put on the 3" lift kit and 33" tires (i have taken it thru some serious mud and offroad terrain, and the trans was submerged a few times). During acceleration it won't shift out of first gear until 25mph at partial throttle or until I let off the gas at WOT. Also when I am on the highway and stomp on it, it will go from 3 or 4th gears down through 2nd right into first, so passing is a pain in the butt. I've partially diagnosed the problem so far. According to a manual I read it is either the 1-2 shift accumulator (possibly broken spring or seal) or the vehicle speed sensor. This weekend I am going to drop the pan, R2 the spring and seals on the 1-2 accumulator, maybe put an oregon corvette servo on also, and flush the thing out. The only other symptoms has been my parking brake and ABS lights will come on simultaneously every couple of days while i am driving down the road. but after a restart that goes away. My current mods that could affect the transmission are 3" suspension lift, 33" nitto trail grapplers, and bully dog GT tuner/programmer. any help from the transmission wizards out there would be helpful! thanks guys!