Royster's advice on the rad clean is solid. If you want to dissolve rust and calcification in the radiator try mixing up citric acid powder in hot water and filling the radiator while it's out of the truck and let it sit for half an hour. It's safe to handle and does a decent job of dissolving the aforementioned. Give it a big flush out afterwards to make sure there's none of the solution left before installing it. You can use the citric acid in the truck but it can be aggressive on alloy if left in there for too long - it will need a very thorough flush out but it will clean out the heater core in the process.