After you complete a good flush of the coolant system and replace your water pump you may also want to consider installing a coolant filter. The 7.3’s are known for having a lot of sand that remains in the block after the casting process. This sand can continue to “weep” out of the pours of the block for years even after flushing the system. The sand floating around in the system can cause accelerated wear on the water pump as well as the rest of your cooling system. Just something to consider. As far as the coolant goes, You will be able to find waaaaay too many post’s that talk about the color/type/brand of coolant to use. Some of the 2002 trucks produced early in the production run came equipped with “green” coolant. The 2002 trucks produced later in the production run came equipped with “gold” coolant. If the truck came with green, use green. If the truck came with gold, use gold. You also have the option of switching to a true heavy duty diesel spec coolant. Again, you will be able to find lots of information (and tons of passionate opinions) about the type of coolant available/recommended for your 7.3. Good luck with your project.