This indicates poor air flow. Just think about the billions of bugs that get jammed in the front of that radiator. And nobody ever cleans it out. If you have access to compressed air, blow through the rad backwards with a nozzle. If all else, use a garden hose.
Then at least you know air is getting through.
Usually the radiator fan is working right. When at idle the car is not moving and no air flow through the radiator. The fan is suppose to provide this flow. It may not be.
When the car is moving there is air flow through the radiator. There are other scenarios but this the first one I would look at.
Low coolant and/or bad water pump would be first things to check. Could also be bad thermostat.
What year is your truck so we can figure out if the electric cooling fans or belt driven fan clutch could be faulty.
typical of a Chrysler product.
