[R C Cola]

Had a bad noise and popped out of gear on a slight hill in 5th at about 55 .
Stopped and went to put in low (grinding and would not go in). Flashers on and let roll back about a foot, played with the stick and in about 30 seconds got it back in gear and eased off, then into 2nd, and 3rd ran the next 10 miles at about 30 mph then tried 4th no problem. Dropped the trailer at the dealer and eased out. Ran fine went into 5th no problem. Drove 350 miles no prob. or noise. Now the only symtom I notice is sitting still, in neutral,
"with the clutch out" it seems to try to catch and move. I can actually feel the truck jump slightly, so far it has not gone all the way into gear by itself, but that is what it feels like. I did not push hard on the 350 home but not totally sure what the problem might be. 95 NV 4500 w/150k on the clock half of those miles were loaded w/RV's weighing between 5k and 11k some 14k .
Syncros are fine, shifts fine, pulls fine without load. How long should these 4500's last pulling RV's ? Ideas ? My next move is to drain oil and look inside one of the coolers. I don't want to buy a rebuild if it is a simple problem.