Pulsing in 4th gear at crusing speed

[Arl37]

Thanks to all for your comments. The truck was originally set at 12 degrees BTDC and when I noticed the pulsing I set back to 4. Still pulsing. Reset TV cable. No change in pulsing. U joints are all new and drive line balanced. Confident there is no drive line problem.
HOWEVER, in the process of trying to get as much road noise ( wheel bearings, ujoints etc) out of the truck as possible prior to painting I discovered today that the rear end is causing all the nosie. Sounds really shot and creates a whup de whump and low speed. I wonder if it could be so shot that it is causing the pulsing in 4th. 4th is really low. Must be 1 to 1 or lower. Would a really bad rear end cause the pulsing in 4th?