Have you tried checking your vaccum lines or checked to see if there was any build up around the TB area? When the bucking occurs, do the RPMs change on the tach?
Does it buck with car in neutral? If it does, then grab a bottle of carb cleaner, rev it like you mentioned and spray the carb cleaner around the hoses and around the seals of the UIM.
If it does not do it while in neutral, then maybe we are talking more along the lines of a possible clutch or contact surface issue.
Just trying to throw around some ideas that might not have been mentioned before.
