I realized as I was driving home from a recent car show (first time I've driven the car since September) that I have developed a significant driveline vibration in the camaro. need to figure this out and fix it before this years track days start for me (April/ May). Here is some background:

1991 Z28
LS1
T56
Stock driveshaft
Stock Rearend

Vibration happens only when on the gas (most noticable cruising at highway speeds). Take foot of the gas and the vibration goes away.

All I can think of is that I converted the T56 from a LT1 style to a LS1 style when converting to the LS1 motor. It didn't have this problem right after completing the swap, but I'm sure it's probably developed over time (I don't drive the car much).

I can't rule out anything yet, but It's unlikely to be the driveshaft or rearend since those are about the only thing left in the car that are stock and original.

Suggestions?

Alot of times, a vibration upon acceleration but not on decel is related to a seized u-joint.

I hadn't thought of that. I'll check on that tonight. Thanks!

If you have another driveshaft you can borrow I'd check that too. On both my stock and race car F-bods I have had to have those rebalanced more than you would think. If this does not pan out then I'd check the wheels for balance.

Check your pinion angle as well. Pinion angle/ u-joint angle typically changes due to axle windup during acceleration. Vibrations can come from the front and back u-joints not having the same angle. Do you have the stock torque arm? You might check your transmission mount as well (make sure the bolts are tight and the rubber/polyurethane is still good). I suppose bad control arm bushings could also cause the axle to windup more than usual, leading to the vibration.