Not a lot heat

90 chyr 3.3 new rad,new water pump , thurmo-stat when at opp temp, top rad hose hot, bottom hose cold.

Check the heater hoses. Are they both hot?

Has your mileage dropped?

Could be a belt…

you mention thermostat. did you put a new one in too? (not just look at and reinstall the old one)

not to be a PITA, but are you certain you installed the thermostat the right direction? this sounds so simple, but it is the first thing to check out. also, are you sure when you were replacing the t stat you threw away the OLD one, and didnt get them mixed up, and reinstall the old one?

Sounds like you might have air in the system . . . is there a bleeder screw on the thermostat housing? Bleed the air out of the cooling system and get a new radiator cap . . the proper one, they have specific pressures. While you’re at the parts store, pick up a new thermostat (they can be bad from the box) and install it the right way. Good luck! Rocketman

one hot going in ,one warm going out.

They should both be hot if the engine is at operating temp and you have good flow. As already mentioned, low flow could be due to an air pocket. It could also be due to a clogged heater core.