The water pump and radiator will be OK because the engine stays cool when it has good air flow form driving. When you stop, the fan should come on and force enough air through the radiator to keep the engine cool. This isn't happening.
I'm not sure if that care has an electric or some sort of clutch driven fan, but either way, that's where the problem is. If it's electic it may be the fan motor, the relay, a sensor or a wwiring problem. But at least you know where to start looking now.
Neither the water pump or the radiator. The viscus drive on the fan blade is bad.
The situation you have described is almost undoubtedly a fan issue. If you vehicle runs with in temp while in motion it is getting sufficient air intake due to your movement. But and idle or slow speed the air intake is much less. Yup, bet you a buck it is a fan problem.
The fan isn't running. Replace the fan relay- $15 plug-in part.
So what year is your truck so we can look-up some parts.
oscillation adjustment screw is loose.
nahd
