I haven't had my 2008 Ford 31M long enough to comment on all of these, but I will say the general consensus I saw out there before buying mine was the V10 is pretty solid. The same motor/tranny combo is in so many commercial vehicles that 100k miles on one didn't bother me, as long as it was maintained. And after looking at what local dealerships were offering for $35k+, I've been very happy with our choice. For $26k I got 50+ pages of maintenance documentation on ours so I know what was done and at what mileage. The piddly things like loose hinges and other little things I've gone over were the same things I saw on the expensive ones we saw at dealerships.
I don't think I would ever chip mine, I just don't think you're going to gain much. It's a 14,000lb box going down the road, so I've just accepted the fact the mpg will be 7-10mpg.
