I recently started getting a vibration around speeds of 65 MPH + and during acceleration. I have an 87 Z28 with an L98 and a reman 700R4. I also have the LS1 alm driveshaft (about 42000 mi on it). I put the car on a lift and held the engine between 2000 to 3000 RPM and got vibration while in OD. I then put the car in N and did the same thing, no vibration. This leads me to believe that the vibration is coming from the drivetrain. I haven't tried the same test with the wheels off, I assume that with the wheels off no vibration would tell me that it is the tires that are out of balance.

My question is, could the torque converter be going out? The trans still shifts fine through all gears and does not slip. Any help is appreciated.