Did any of the vacuum lines get removed when you were replacing the T-belt?
You might also check for cracks in the vacuum lines. Idle surging when breaks are applied can also be from a vacuum leak.
What is the rpm at idle? An idle that is set to high can also cause a surge when sitting at a stop w/the breaks applied. Both my 3.0 and 22re will do this if I don't re-adjust the idle when done wheeling. I usually set the idle higher than normal when wheeling to keep the engine from stalling out when crawling.
