The military wreckers are incredibly versatile and useful. I spent $5300 for mine when I bought it from a friend, we got it running about a week before that. This one needed quite a bit of work and still has more to come. He replaced the fuel lines, filter, rebuilt the primer pump, bought new brake lines while he owned it. I've repacked the wheel bearings, replaced 1 wheel cylinder and all seals on all 6 hubs. Replaced the PTO shaft that powers the crane, got the transmission PTO working again for the front winch, added a coolant filter and changed coolant, change trans fluid, removed part of the front winch cable (needs replacement), replaced the brake master cylinder, upgraded to the 395x85x20" tires (47" tall), and swapped out the seats.
I need to repaint the truck, fix some rust on the cab hard top, change the rest of the fluids, and that should be it. A wrecker in great shape out here sells quickly at 15-20,000.
The older 5 tons such as the m39 series (Vietnam era, like my M51 dump truck) and the M809 series (my m816 for example) have the 5 speed manual transmission. 1950's-1980's have the manual. The newer M939 series has a auto transmission and air brakes.
I called it quits on the deuce after the stock engine and transmission were out of the truck. Between the planned power upgrades for the DT466, a new clutch, a replacement transmission, power steering parts, a backup brake system..... I was looking at about $8,000 to get the truck how I wanted. Going to a 5 ton is cheaper for me, at the expense of more weight (13,700 for my deuce compared to roughly 20,000 pounds for the 5 ton) and lower fuel economy because of that weight.
From experience I don't recommend using a pickup to tow your m109 back if you have problems. The brakes in the deuce work without air, but you have no power assist once the air is gone. I was standing on the brake pedal to get it to stop. With your location there are many people on steel soldiers there that can tow you if necessary.