Get someone to sit in the driver's seat and cycle the steering wheel while you look at every item in the steering system. Also while there look for things like broken leaf springs, loose or broken shackle mounts, etc.


That would be a place to start. If you still think it is in the drivetrain, jack up the rear axle, put it in gear and have someone else carefully observe the running gear.

Ed

'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.