With the truck sitting still, what rpm will it wind up to when you floor it? It should jump to the governed rpm of 2750 and hold. If it doesn't, then you have more work to do.
The resource secition at the top of the page has links to manuals. There is a great manual called "Trouble shooting manual LDS-465-1 Multifuel engine." Let that be your guide.
By the way, I drove my M35A2 about 140 miles Saturday. It ran like a top until the last 30 miles. I slowed down for a turn and then couldn't get back up to 50 mph. A storm was blowing in and we were going into the real strong gusting wind and I figured it was that along with a slight up hill grade. Flat land and a tail wind followed with no more than 2200 rpm in any gear. I pulled over to check for locked brakes, smoking hubs and to drain the primary fuel filter. No troubles found and it ran the same. I went on home at a slower speed. I let it sit for a few hours while I cooled off. Draining the secondary fuel filters had me revving back up to 2600 in any gear again. I didn't see anything come out that looked bad. The point is yours could still be filter related.
