HI, I have a 2001 g3500 with a 6.5l, and I am experiencing a overheating problem while climbing hills. I will heat up fairly quickly on a climb, and cool quickly on the other side. I have flushed and cleaned the radiator, installed new thermostats, and replaced the fan clutch, but it still does the same thing. if it gets hot, and I pull over it cools from 235 to 190 in about 5 min of idling. wondering if anybody has any Ideas, thanks

 

Did you confirm that fan kicks on when it should? I think you can test by turning A/C on full blast.

Did you test or change the radiator cap? It's important that the system maintains 15 psi or so.