09 chevy 3500 6.0 runs 210 except at idle SOMETIMES. 50% of the time it will stay at 210 then others it will go up to 230 or so. Get this. Turn the heater on it gets hotter at idle. Replaced the thermostat twice, swapped out temp sensor. Flushed radiator. My local service guy threw a temp gun on it and said that the radiator is partially blocked. IF thats the case whats the best way to flush it? Or just buy a new radiator. If I knew 100% it was the radiator I'd buy one. I think bronco72 put this rad on a couple years ago. Thoughts?