[s-cars] Vibration

[RGuzz]

94 S-4, 92k miles, still with vibration, or shudder, on take off, also 
noticeable to passengers. Feels like it's underneath the car, in the 
drivetrain somewhere. Seems most noticeable in first and second. I went 
over the car with my mechanic and friend including a look at the front 
end and axles. There appears to be no play anywhere. We haven't looked 
at the driveshaft yet. Shifting appears to be perfect without play or 
clunk, clutch is fine. Engine, tranny mounts look okay. Don't feel it at 
interstate speeds.
How do I troubleshoot the driveshaft? What should I look for? How high 
on the problem list should the driveshaft be?
Plugs were fine. Suggestions?
Thanks,
Rich