Do yourself a favor and never buy a 6.0 ford diesel truck. We're stuck on the side of I-10 in Arizona trying to jb weld a crack in my coolant reservoir.
get a 7.3.. my brother has a 6.blow and my father has a 6.4.. both trucks have seen the dealer plenty of times. my 02 7.3 on the other hand is creeping up on 800k miles, never seeing the dealer, and still runs like new with mods
dude if it still leaks then leave the cap partially open so it doesnt build pressure, it will still cool and shouldn't overflow too much as long as you stay out of boost.