Transmission or differential

No help from me. I was going to suggest u joints, but see you've already replaced them.

You might take a look at sway bar bushings, but they would give the same symptoms warm or cold. Low transmission or clogged filter could do it, but only with an automatic, which you wouldn't have or you wouldn't have replaced a clutch.

Sorry for the lack of help.

Its the differentials. Its an old 4Wdr., so it has two. The vibrations might be coming from the fact that when you turn it the front wheel drives forward while the rear wheel pivots, thus putting a great deal of stress on the rear differential. The cure is actually to turn more gently and in a wider radius and if you feel the vibrations or clunking (gear teeth jumping from too much torque) straighten out and go slower. The old Dodge Power Wagons at diffs and trannies for breakfast which is one of the reasons they're only totally restored collectors items. Today's all wheel drives use computerized limited slip differentials. But none of them can yet deal with a 'lock to lock' situation. I surely am glad I didn't use my '67 F-250 Ranger as a recreational vehicle. Lastly, if you are not an expert transmission specialist ASE, you might save yourself grief by seeking one. There are not too many ASE certified Master Mechanics with all quals, but I bet there's at least one in your city. Or find yours online at the ASE site.