99 WS-sick

iTrader: (2)

i have a 99 T/A, at speeds above 80mph in a straight line the brakes pulsate (not pedal), just the brakes, the car pulls side to side. if im going into a turn and i hit the brakes to hard the car pulls side to side. if i hit the brakes going over dumps the "lowtrac" light comes on but im not sliding or locking up the tires. and when i slowly come to a stop, SOMETIMES not all the time, the car will pull to one side (its not always the same side). i can feel the pedal get stiff and then it feels like it releases some presure and everything goes normal again but it only does that if im standing on the brakes (feels like im gonna break the pedal). i have 17inch wheels in the front and 18inch wheels in the back but the outside diameter is basicly the same. its worse between 120-150 mph. im thinking its the abs but im not sure, the calipers have been changed and the rotars are not warped. any advice will help