Is Prestone Anti-Freeze ok to use in these trucks?? I don't have access to much else.

 

With any anti-freeze, including Prestone, just make sure it is the low silicate. I use the Fleetguard. Any Diesel parts facility should be able to get it for you. The Fleetguard Complete brand is premixed and the newer version is the extended interval (600,000 miles) if you want to go that far.