One thing to think about is how these trucks are built...very high gear ratios, slow speeds mostly. They accrue more wear and tear than a civilian vehicle of the same size. Everything that turns turns faster but goes slower than your regular Peterbuilt.
Newer 5-tons notwithstanding, they seem to have a great OD system for decent highway speeds.
Push an M37 or M54 for over 100K miles and you will learn all about worn out parts. I see the usual life of a tactical is around 15K miles before it is sold off or rebuilt.
My '67 M54A1 had only 22K on the clock, and was rebuilt twice (Sagami, Japan 1973 and Nurnberg, Germany 1985) before Desert Storm and then sold to me.
Dennis