One other problem my truck has is when I am driving down the road it starts to get a really bad roaring/droning noise between 45-50 mph. I can feel a vibration on the floorboard when in starts. it gets loud enough you almost cant here the person talking in the passenger seat. All my U-joints felt ok to me but i will recheck them. The carrier bearing feels like it might have a little play in it and will have to recheck that too. I retorqued the bolts on the driveshaft coming out of the transfer case and put thm in with locktight blue. Any help would be awesome.
The truck is a 1999 F350 CC DRW 4x4. Only mods are an aftermarket muffler and a superchips tuner. truck has 286k.
no vibration in the steering wheel? check rear wheel bearings and things of that nature!!! also if you have the space securly block the rear tires off the ground and have some one opperate your accelerator pedal in gear running and see if your drive shaft has excess play in motion!! i myself believe you have a pinion bearing going out!!
When you checked the driveline U-joints, did you remove the driveshaft? I had a U-joint that was completely froze up but I didn't know it was bad until I removed the driveshaft. It showed no signs of damage while on the truck but as soon as I removed the driveshaft it was very obvious...I couldn't move it by hand!!
It made a similar noise that you are describing. Good luck!