Have have a weird problem I need help!! My truck has 141,000 miles on it. Runs fine. Last year pass smog no problem. This year it did not. The mechanic I took it to said the lower radiator hose was cool and the upper was hot. Temp gauge is where it always is. Mechanic says water pump, I said no way. This is list of things I have tested. Let truck warm up for 30min. Throttled it up and checked upper/lower radiator hoses to see if they collapsed. (No) Popped cap off radiator looked for circulation (Very little) Removed thermostate and tested in boiling water. (Worked fine) bought a new one and tested worked fine. Left it in buttoned it up. Removed old water pump, looked like it was new from factory, radiator- filled and let water flow though it. (Fine) This truck has been babied, no leaks anywhere. All fluids are clean. No work has ever been done on this truck, only oil changes transmission and gearbox fluids has been change by me. Not sure what’s going on.