My truck has been running hot lately when caught in traffic jams at low speeds or stopped. Once I start driving faster it seems to cool back down.
Today it red lined on hot on the way home from work, but did not overheat. Heater also won't warm up when idling in driveway, only when driving. I need help figuring out the problem.

 

You are low on coolant, and likely the fan clutch is failing.

 

Thanks...already checked the coolant level and it is good. I will check the fan clutch. Much appreciated.