I'd remove the track ball from the mouse and look at teh 2 wheels that the ball ride on...is there grime on the wheels. If so remove grime with q-tip and then clean ball, and when ball is dry place back into mouse and lock the quarter turn ball retaining plate and see if that helps.
If it doesnt help, buy a new mouse an optical is better and you might have trouble finding a ball mouse anyways.
If that is still an issue then are you eating up all the bandwidth on the USB port, such as is your internet connected via USB instead of Ethernet in which you have a saturated USB channel.