Sounds like you should do a complete tear down, make sure ur diffs r built correctly, take all ur servos out center them thru ur transmitter and put them back into place. Also make sure ur belts move freely at all times. Id check to see that theirs no binding in the sterring when you move from right to left. Ive seen people move from right to left and then try to turn the wheels and theirs minor binding which in turn will give you jumpy turns in and out of corners. make sure ur receiver pack is charged and servos have correct clearence. Just go over the car again and see what you come up with
Good luck, keep plugging away!