[84LX89GT]

Does your engine cool off at all when you're driving highway speeds compared to at a stop or does it do the opposite, or does the temp stay the same no matter what?

You could also pull off the water pump (gaskets really aren't that expensive) and make sure that the impeller is still intact and that it is actually flowing coolant.

How do your radiator hoses feel? If the bottom one is cold and top one lukewarm there's probably a flow problem somewhere in your cooling system, probably your radiator or corroded water pump impeller, hopefully not a rust blockage or something in the engine.

One thing you could do just to see if your radiator may be plugged is to take off both hoses and run water through the top and see if an equal amount comes out the bottom, or if it flies back out the top again. I had a radiator blockage when i had an 84 5.0L and i'd pull the bottom hose and it would only allow a fair amount of coolant to escape, just enough coolant to keep the engine from going nuclear, when i'd fill the top hose it would run out the top.

Good luck, hope some of this helped in some way.