2002 pontiac montana coolant temp

Things I know:

* Coolant Temperature Very Hot
* Coolant Temperature Warning Light Goes On and Off
* Radiator Cap is cold
* Hose coming from right near radiator cap is cold
* When heat is turned on inside the van cold air comes out vents at low RPM (3500-)
* When heat is turned on inside the van warm/hot air comes out vents at higher RPM (3500+)
* When heat is turned on inside the van at high RPM (3500+) with warm air coming out vent coolant temperature does do down

I believe the thermostat is to blame.

Please confirm. Thanks

I believe you're right.

Circulation isn't happening.

Are you sure it's not the water pump? It sounds like the water pump vanes may be corroded off and it's not circulating coolant until it's at a very high rpm.

I was curious, has the issue been resolved?