We work on a ton of hotshot trucks from our forest service, quite a few are 6.4s, and are a major pain in the ass to work on, and they fail quite often. Majority of them are backup trucks for the 6.7 and cummins trucks. They are currently in the process of phasing most of them out, and i think there is only 1 or 2 6.0s left. Dont know if that helps your decision at all, but good luck.
Most of the ones that are chase trucks like you seem to be looking at, are gassers around here.
I can confirm the above statements. The 6.0 and 6.4 fleet on our forest is mostly phased out. While those trucks were in our fleet, they were constantly in the shop for repairs. Injectors and turbos were the biggest portion of work being done. Most of the trucks were on their 2nd motor when they went up for auction.
The 6.7 Ford and Cummins trucks that are in the fleet are holding up better. We don’t have any patrol/Type 6 outfitted trucks, they are all the HotShot Supt, or Dozer Tender outfitted trucks.
However they are not problem free. The fire environment and the operators that run them are pretty tough on them. We’ve had issues specifically related to fuel quality, and air filter maintenance. We had a few of the early 6.7 fords with tranny issues, but the OEM updates fixed that. In my anecdotal surveys, I’d say the oil change interval is way to long on our trucks too. I’ve seen some go 10-15k between changes.
If it was me having the experience I have I’d do a model year 15 or newer 550 or 5500.