Driveshaft hard to turn sometimes

Starting this week, the driveline started to bind up, that is, hard to turn sometimes. It comes and goes as I can feel it in the throttle (more fuel needed) and in the shifting, and at times it seems to "free up". It does it loaded/empty and is not road speed or throttle dependent. When stopped the truck does slightly roll, even on the slightest incline. The big clue is the rear diff. temp gets to 225 degs and climbing, the front diff. to 175, usual temps are 125 to 150. The tranny temp doesn't rise much. When stopped, I try to hand turn the driveshaft and can not do it, absolutely no free travel at all. During the "freed up" times I can turn the shaft slightly. The brakes aren't hanging. I was told by a reputable rebuild shop that the rear diff. (700K miles) probably had bearings going out. Today, I pulled the diff. and all seemed fine; free turning and very little rotating noise. Also I noticed the driveshaft had it's usual play. I replaced the rear with a totally rebuilt unit and it did NOT fix the problem. About 6 weeks ago, I replaced the front diff/power divider with a completely rebuilt unit, no problems with it since. So I've spent over $2000 today and STILL have this problem. Any ideas on the cause of this?

 

The diff temps still run abnormally high after the replacement. I believe the rear temp (the replaced one) would peg the gauge, 300 degs, if I would continue to drive it. The rebuild shop is high reputed, being in business for over 30 years. It is one of the largest suppliers of rebuilt driveline components in this area. About the trailer question, this condition exists in all situations, empty or loaded trailer and even bobtailing.
Today I'll drop the in-between shaft and drive around slowly. This should help me isolate the problem.

 

I can understand a slight temp increase but 250 degs. and climbing? When I replaced the front diff/power divider about 6 weeks ago, I didn't have the heat buildup. The front diff ran at the usual 125-150 degree range. About the tranny possibility, could the seizing gear release from time to time? My condition comes and goes, even driving it. Shouldn't the tranny temp run up also? It doesn't get over 140 degs.

 

The oil sample sounds like a good idea. I've checked the brake temps and they all are cool even at interstate speeds.