Gary,
Keeping up with the change schedule for whatever type and brand of coolant you use is more important that which one you put in your truck.
In spite of the above, it should be ethylene glycol type, as specified in the owners and service manuals.
There are extended life coolants available that don't require changing as frequently as standard coolants. Another advantage to this type is that at the first "change" interval, you merely add a bottle (or less) of extender and keep on driving. The extender replenishes the corrosion inhibiters in the coolant, but you can only do it once per fill. At the next change interval, you must actually change the coolant.
I think that Cummins is now selling an extended life coolant. If you can't find some there, check your local Caterpillar dealer. That's where I got mine. I bought it there because the Cat dealer was the only place where they stocked the extender.
I bought the pre-mixed coolant. I did the math and found that it was cheaper than buying the concentrate and adding a gallon of distilled water.
Good luck.