Have a 91 firebird with a t5. Backstory last motor was knocking but had no other real problems. Put a new sbc in it but with a carb of course. Car has been doing fine for about a month now. Last weekend I drove 250 miles home, had a slight vibration so replaced U joints on both ends of driveshaft with moog. Broke them in by doing donuts in a field. Went on a drive and had a death wobble starting at 65mph and getting worse at higher speeds. Thought the moog u joints were junk so popped them out and replaced them with spicer. Still wobbles. It’s more of a violent vibration. It’s most noticeable holding the shifter. Gets worse with more speed. Can’t figure out for the life of me what it is. When it starts shaking you can hold the clutch in and put it in neutral and it still shakes until you slow down. Car also shakes letting the clutch out into first gear and reverse