Maybe you have a torque tube bearing that is seizing up.

Edit: After re-reading your first post, I would guess something wrong inside your transmission.

 

If that were the case, then the idle would probably drop a little with the clutch connected and the transmission in neutral.

My vote is for something related to the clutch causing the trouble.

 

If it was related to the clutch not disengaging all the way, it would grind going into reverse. I don't think its the hydraulics or a bad pilot bearing. Somebody mentioned the torque tube but I would think that would be making some sort of noise. Tough to diagnose this one without being there.

 

I have been following this post for a while, from the info we are getting it's a tough one to figure out. So I guess I'll put in my 2 cents.

If the trans is in neutral and the clutch is out, the separation between the rotating parts and the non-rotating parts occurs in the trans (on the mainshaft). If the clutch is pushed in (whether it's in gear or not ) the separation between rotating parts occurs in the clutch (the engine, flywheel, pressure plate are turning, the disk input shaft, trans etc. are not.) If there is drag when the clutch pedal is out the problem has to be on the main shaft (bushings and bearings ) Bad bearings / bushings also cause shifting problems.

Another answer to this problem is just keep driving it will show it's self after a while.