shutter

I know this is probably on here, but I have looked and looked and cant find it. I bought a blue msp with 118k on it, the car blew an engine last year and i have receipts from the rebuild from mazda for almost 8k dollars. the new motor/clutch/timingbelt.... (you get the idea) only has 3k miles on...

I've got a 2002 mazda protege 5 speed manual with a bit over 105,000 miles on it and i believe the first clutch. After the car gets good and hot, it shutters (vibrates the hole car violently) when letting the clutch out in first gear. I am absolutely sure I am not lugging the engine because it...