Sounds like you need to back flush the radiator if that hasn't been done.
And in actuality, running straight water in a vehicle in the summer time is the best heat transfer method. You just need to add chemicals to it to insure the water pump is properly lubricated and the metal is properly protected. Marketed as "Water wetter if I am not mistaken. Water boils at a lower temp than coolant does but coolant does not transfer heat nearly as well as straight water. Straight water is very corrosive and can damage the water pump since it is used for a lubricant as well.
Another potential issue, and one I have had on my own vehicles...
Has tap water ever been used in your truck? City tap water can have chemicals in it intended to coat metal piping to prevent it from leaching out lead. (See Flint, MI for details of what can happen when this is NOT put in the water...) If this is the case then you may want to get some distilled water and perform a full system flush of your radiator. You may need to do a couple full radiator flushes to get all of the phosphates and such out of your coolant system. Use only the distilled water to flush the system out. When you refill only use distilled water (Or better) to fill it back up to make your proper mix of coolant.
Worst case, replace the radiator but a couple bottles of coolant flush is much cheaper.
I used to have this issue with any vehicle I had that was higher mileage and flushing the radiator did wonders. The heat transfer is the most important part of your coolant system. If you are using well water that leaves stains on stuff and you put that in your vehicle you will coat your radiator and internal water passages in your engine. This prevents the heat transfering from the engine to the water allowing the engine to run hotter, this also prevents the heat to be released into the radiator. If you had your radiator flushed and filled since last summer or possibly even from the water pump change if they used tap water could have added enough coating solution to cause your problem.
Also note, in early dexcool systems there were clay tablets put into the coolant. These tablets were to prevent leaks and if air got into the system they clumped up and caused plugs in the system. If you had the original dexcool in your system it is possible that a back flushing of the cooling components may be required to get your system back to normal. But never use tap water in your cooling system except for dire emergencies.
And in actuality, running straight water in a vehicle in the summer time is the best heat transfer method. You just need to add chemicals to it to insure the water pump is properly lubricated and the metal is properly protected. Marketed as "Water wetter if I am not mistaken. Water boils at a lower temp than coolant does but coolant does not transfer heat nearly as well as straight water. Straight water is very corrosive and can damage the water pump since it is used for a lubricant as well.
Another potential issue, and one I have had on my own vehicles...
Has tap water ever been used in your truck? City tap water can have chemicals in it intended to coat metal piping to prevent it from leaching out lead. (See Flint, MI for details of what can happen when this is NOT put in the water...) If this is the case then you may want to get some distilled water and perform a full system flush of your radiator. You may need to do a couple full radiator flushes to get all of the phosphates and such out of your coolant system. Use only the distilled water to flush the system out. When you refill only use distilled water (Or better) to fill it back up to make your proper mix of coolant.
Worst case, replace the radiator but a couple bottles of coolant flush is much cheaper.
I used to have this issue with any vehicle I had that was higher mileage and flushing the radiator did wonders. The heat transfer is the most important part of your coolant system. If you are using well water that leaves stains on stuff and you put that in your vehicle you will coat your radiator and internal water passages in your engine. This prevents the heat transfering from the engine to the water allowing the engine to run hotter, this also prevents the heat to be released into the radiator. If you had your radiator flushed and filled since last summer or possibly even from the water pump change if they used tap water could have added enough coating solution to cause your problem.
Also note, in early dexcool systems there were clay tablets put into the coolant. These tablets were to prevent leaks and if air got into the system they clumped up and caused plugs in the system. If you had the original dexcool in your system it is possible that a back flushing of the cooling components may be required to get your system back to normal. But never use tap water in your cooling system except for dire emergencies.
