out of curiosity, did you replace the pilot bearing when you did your clutch? mine went on my stang and it vibrated, though not nearly as bad as you make it sound. Remember, when problems happen, its not necessarily 1 thing that went wrong, but a collection of things. What rear end and tranny do you have? could be you bent your output shaft of your tranny (did you check your yoke when you did the u-joints?) the absolute last thing i can think of is when you hit the curb and came down busted a bushing in the rear, you would coast fine but when you hammer it or accelerate the torque would make it vibrate