They all have 4.56 except the M1009 or Blazer, those are 3.08. A 12 valve would be awesome in a CUCV and you can probably find the proper adapter to run the original transmission. Glow plug issues are probably the most common, followed closely by fuel issues. They are bad about leaking down from several sources. I think block and crank failures can be traced back to too much rpm. The main bearing webbing cracks and when it gets loose enough, you can not keep main bearings in the engine. What makes the truck so beautiful is the smooth economical diesel with a gear ratio low enough to get a lot of work done, unfortunately, that is part of the downfall for many, due to continuous high rpm running. 6.2 diesels in 1/2 ton applications and overdrive transmissions frequently made 300,000 miles with few problems. 6.2 diesels in low geared towing trucks were lucky to see 100,000 miles, normally blowing oil and seals. We know they will run a long time at 1800 to 2200, the range they were designed to run. How much rpm over that they can stand and how long they will last depends upon who you talk to.
My M1008 is low mileage, around 32,000 now, it normally does not use or leak oil. Run it hard for a few hours though and it will be dripping when you stop and will use a quart in less than 1,000 miles. We leaned on it pretty hard trying to make a scheduled appointment in Jefferson City for my M1009. We tried to sneak in between snow storms and the GL rep's doctor's appointment. I left town early enough, but left my paperwork at home and had to return for it. We drove 60-65 for seven hours and she was puking oil when we got there. 60 mph with a 32" tire is roughly 3,000 rpm.
My 2003 Cummins would rin over 3,000... 3,300 I think... my old 93 12 valve was governed at 2450... which would make a M1008 a less than 50 mph truck on the governor, with the stock transmission. Stepping up to a 36" tire would be a 56 mph truck in this application. Glen
