Cusser
+1y
That's called the "double-whammy" !!!
If it overheats in town/traffic but is OK while on the freeway, that is indicative of a bad fan clutch. I've gone through those about every 6 years here, can affect my AC operation too.
Thermostat is on the passenger side of the cylinder head, the housing is connected to the upper radiator hose. I jack up the front right end of the truck so the thermostat will stay in place, as it goes in vertical, with the toggle pin at the top. Make sure the water outlet side is flat, and don't overtighten.
I use a 190/195F thermostat (O'Reillys or CarQuest, can't remember) even in our climate, as I couldn't get decent heat in winter with a 180F T-stat. If you end up needing a radiator, you'd likely be OK with a 1-row as yours doesn't have AC, but the all-aluminum 2-row ones through O-Reillys do work great, and are only like $15 more. Better do a good radiator chemical flush as yours is getting to that age. I also jack up the front end and run it while filling with coolant because these are a little tough to bleed out all the air.
Important thing is: don't let it run hot over the range, or you'll be doing (at minimum) a head gasket !!!