I have a 96 F250 2WD auto. When I back up I feel a shuddering all over truck, especially noticeable when turning with a load. Replaced u-joints and slip joint seemed well lubed. It has a C9 rear axle. Any ideas?

 

Just a guess but possibly the limited slip differential clutches chattering. Maybe drain the diff, refill with fresh gear oil and the friction modifier.
Another possibility is that the reverse clutches in the transmission are slipping. Check that the fluid level is good and check the color and smell of the fluid.
Also check that both engine mounts are good.

 

Thanks. I will check it out