[Fourtrail]

Correct water pump? Not the serpentine reverse rotation, because that will do what you are talking about. Also not air locked? can you see good flow with the radiator cap off when it get to temp to open up the thermostat?

 

[Fourtrail]

258 could be factory with the serpentine belt. unfortunately you have to pull the pump to verify as the part number on the water pump body is the same for standard and reverse rotation.


Have you shot the radiator hoses with an infrared temp gun? verify what the temps actually are? shoot the heater hoses and the intake where the water jackets are.