Nissan Repair: out of balance, drive shaft repair, twcny rr

Question
I have a Nissan Frontier ex cab pickup.
I have had it back several times to the
Dealership for an out of balance problem.
They have done the tires and the drive shaft.
It still has a bounce that feals like a tire
out of balance at 40 to about 55 MPH.
Tire balance or drive shaft repair did not
help. What else could it be?
Please help me nobody seams to know what
to do.
                         Bob Scofield
                   rws404@twcny.rr.com  

Answer
Bob,

Have the dealer put it on a rack and have a mechanic run the drivetrain at the speed you indicate.  I had a Mustang that had the same problem as you describe and it turned out to be a defective universal joint.  Until it was up in the air they could not figure it out.  When the service manager and I looked while the mechanic ran the car it showed up.  It had been driving me nuts for weeks and several trips to the dealership.  Let me know how it goes.