1. never flush a tranny unless you have changed the filter first, this seems to be a very common problem with shops that don't do tranny work , the tranny computer is also known for failure on them, if fluid smells burnt than most likely its on its way out, also if too much friction additive is used it will cause slippage and tranny overheating, the friction additive converts Dextron 3 to Dextron 4 which helps soften shifts and prevents torque converter chatter.(some shops use posi differential additive which is same as the tranny additive but less expensive )