Water Pump Problems
I had rebuilt my coolant system completely two years ago. You are helping yourself by replacing that clutch unit, and belts on your motor. Incidentally you may also want to completely substitute the type of anti-freeze that you are using.
There are some coolant types that are a lot easier on the systems used in these trucks. These trucks have aluminum fins, plastic caps, and steel blocks, and aluminum head gaskets. I had completely converted my new system to the Prestone, Long Life Coolant. This is the "Orange" colored variety.
The system must be completely flushed, and filled. After replacement you must never use the "Green" Glycol coolant again.
It is not good to mix the coolant types.