Durango overheating question.

I know its not an a body but I figured lots of members either own or wrench on them. I could try a Durango forum but most seem to focus on the mud and manly side of things lol!

Anyways her goes. Is a 2002 Durango AWD with the 4.7. It has randomly overheated and puked out the coolant. I changed the stat and once refilled with coolant it ran fine for months,summer or winter. Then it would randomly overheat again. Refill and away we go for another few months. Until today it only happened to my wife and daughter so I never got to see the symptoms. I have been religiously checking fluid levels and they stay fine.

Just did it to me today though so I got to check it out.

Started truck (+8c here in Canada today btw) and drove away. Minutes into drive Gauge says 1/4 heat but no heat in cabin. Just blowing cold air..... Hmmm.. 1 minute later warning on dash and gauge close to red zone. Let her sit and cool and limped 1/2 mile home. Still hot in laneway running but checked a few things.

If you crack rad cap fluid comes out instantly.

Upper and lower hoses only warm.

Rad cool to warm.

No white smoke or poor performance.

No pump bearing noise.

Oil looks clean.

No evidence of loosing coolant.

Clutch and aux electric fan running.

So I'm thinking coolant not circulating. That points to thermostat (recently replaced) or water pump. I can replace the pump but since its so random i wont know if i fixed anything. What I don't understand in them working fine for months, quitting then brink OK for another few months. Ideas I'm baffled.