Check for a blown head gasket! Sorry.

Subject: Overheating
I've got an 82 diesel, she's overheating. On 5 hour road trip, after hour 4
started blowing cold air then back to hot, then cold again. Soon the needle
raised up and light flashed. Had extra coolant with me, while topping off
expansion saw that the cloth wrapped hose to fill tank had come off.
Replaced and gingerly made it to destination. Stopped three times to let
cool. I figured I'd gotten air into the system and needed to bleed it out.
I've done that today--with little success. Got it up to temp, parked on a
ridiculous incline to get the air up to the radiator. Not much hissing.
After 8 attempts only once did coolant bleed out. Air continued to blow
mostly cold with heat cranked, occasionally while driving around it warmed a
little. Needle would raise at low RPM's then return closer to the middle
when I revved it up. Even at slower speeds with engine revved it would
cool--that confuses me a bit as little air is moving over
 the radiator--makes me think it'd be hotter.