Sorry to hear about your issues. It's odd that the 370XP works in the truck and not the van but there is a difference between the E series and the F series. On the trucks the alternator is PCM controlled.
I did have an issue when I installed the 250XP from DC Power. There's a crucial wire that reports back to the alternator about the voltage it's putting out. The OEM alternator doesn't really put out enough amps on our rigs, or on a 6.0 for that matter, so it's always working overtime. What happens is that wire gets more and more resistant to voltage and then the alternator thinks that it's not putting out enough voltage so it compensates for the bad wire. That kills the alternator. The wire is for the regulator power for the stock alternator. (Lots of current through a small wire for a long period of time = heat. Excessive heat = damaged wire = added resistance). Maybe this is not an issue for the trucks since the PCM is doing the work that the regulator is doing on the E series? At any rate, the end result is it can create issues with a higher amp alternator on a proper voltage feedback.
As for heads, the 6.0 is known for cracked heads. The walls are thin. If it happens to me I will either go with Kill Devil heads that are a new heavy duty casting https://kcturbos.net/collections/new...cylinder-heads
Or, o-ringed heads from UCF machine. https://store.ucfmachineshop.com/sho...-stroke-diesel