around town the trans up shifts just fine..breaks the tires loose very hard on the 1-2 with no problem...however..occasionally ill come to a stop and attemp to power brake the car. It wont even come close to spinning the tires over. Other times it will. Most of the time it wont though. Trans was rebuilt around 50K miles ago and has a tune, stock stall speed, servo and billit trans pan. Also if it could be the same thing. On the interstate there is no "5th" gear..obviously im referring to the convertor locking up. Could this be the lock up soliniod? i was told it also controls down shifting. Please help