Hey guys, i do a lot of canyon driving in my 08 Impala SS. Sometime ago, i lost ability to engine brake. When am in first or second, the car will simply idle rather than rev high rpms and slow the vehicle down. If i give the engine gas, it will rev up to the engine speed and once matched, it will accelerate again. However, it works normally in 3rd gear. I hope this makes sense because i am at a loss. If it makes a difference, it's the 4speed auto. 5.3l LS4 and i have had the transmission fully rebuilt with all the performance uprgrades possible. This started doing it after the rebuild and it hasn't effected vehicle performance other than not being able to brake. I don't want to deal with the thieving trans shop and be jerked around with my "waranty" so if i could get information on what it is i can fix it myself. It's now probably done this for 2 years and I'm just tired of replacing pads so fast. Thanks for any input.