Nope...PT tractor and then Reg number the USAF hasn't used M series designation for quite some time. It makes it hard to find a truck on the line but after a few months you can take any reg number and now exactly what truck it was. I think the PT trucks are numbered 81BXXXX, 91BXXXX, 03BXXXX, etc. However they are a special purpose truck so the alpha code maybe different, I just can't remember and I don't have TO 36-1-191 on me.
I can still tell you 88B3442 and 86B0009 were 7.5ton 6x4's the latter being a GMC Topkick and the other an International 7500. That Topkick was one pile of rolling crap by the time we turned them in.
As for the PT trucks, if you get one it has been through **** and back. The 81 were rode hard and put away wet for nearly 30 years. During the winter in Minot they run them constant, and missions lasted up to 16hrs. They went through APU's and engine rebuilds pretty darn fast.
After 2003 the USAF replaced them with conventional cab models as US manufactures no longer make COE trucks. Unfortunatly due to a specialized trailer requirement they need the same rear spacing and with a conventional cab the wheelbase grew 4 feet. Not only did this mean they don't fit in the AS&I building utilizing the standard load opt, but they can't turn around on site.
The entire conventional fleet is reserved for secondary duty status, hauling PMT, EMT and the occasional Boeing modified PT trailer. The MMT units still relay on the 91 and 03 models for PT missions, here at Minot not sure about other units. All the 81's are gone, I never even saw them go through GL...Had the option to bid on a few APU's over the years but it's kinda specialized power and not something I can use right now.