Bucking Car??

Ok here's the deal, I have a Fiero, with a 3100 from a Grand Am 95, was running like a dream till yesterday, now when I start off in 1st the car will start bucking(like it was in Third), engine revs get erradic, but everything is peachy again when I push the clutch in, I can still move while riding the hell out of the clutch, but problem is still there even as the car speeds up if I let the clutch out all the way. Idea's? Help......