Driveshaft or Rear-end

[UglyFast88]

Hi all-

Got my car together, and it runs incredible. Now I have a question... I'm getting what seems to me to be a foreign vibration through the shifter (Steeda Tri-Ax) starting at about 2100-2300 rpm. I also am getting (sometimes) a shuddering (best way to describe it) when in reverse, and rolling backward, kind of like a kitchen chair "stutters" across linoleum. (like that description?!?)

Last year, I put a set of 3.73's in, and it had the vibration, some howling at higher speeds, but not the stuttering. I also have the original driveshaft in car, with about 150,000 strong. The vibration is bad enough, for instance, to bubble tranny fluid out of the overflow when the tranny is filled, (like after my install- filled to the rim!) but not major enough to cause a real leak once the level gets to the proper level for operation.

Questions are, has anyone run into this? And do you think I'll grenade my tranny driving it like this for a few weeks? It's really not that bad, but I don't want to hurt my car. I'm just not sure how much of it is theshaft, the gears, maybe the T-5, or even the motor or exhaust. My exhaust contacts the frame under normal operation, and that vibrates, too!

I have a T-5 rebuild kit, and an aluminum driveshaft to go into the car in the next few weeks, but what do you think about the gears? Would gears do this- or am I just more worried t I need to be?

Thanks for your help!