The original M35's had Gas engines and a 3053 5 speed transmission. The shift pattern was like this:
r 2 4
1 3 5
5th was a direct 1:1 ratio. The Gasser engines have like a 3400 red line by the way.
4 parts are changed in the Gasser transmission to make it a 3053A. Basically the Gasser 4th gear is made into an overdrive gear and the shift pattern is as described a few post up like this:
r 2 5
1 3 4
So, when you are driving your multifuel engine with a 2850 rpm mechanically imposed by the governor in the injection pump rev limit. You are actually jumping a gear going from 3rd to 4th if you think of how the transmission was originally designed and used. The gear change was needed so the diesels could keep up with the Gassers. Being the government, it was done on the cheap.
Having written all of that out. Which is true and factual. I have to inject a tale a guy just back from Iraq told me at a Boy Scout meeting I drove the Whistler to. He started off "I like the truck. Will it do 65-70?" Uh, no, it pretty much tops out at 56 indicated and I just drive around 48-50 so I don't put a window in the block. "Well, we had a guy in the motor pool who would switch a few gears in the transmission and our trucks would run 65-70 all day long. Nobody ever beat us anywhere." I asked for contact info or a description of what they did. He said no problem and I haven't heard anything since. He believed what he was telling me is all I can say.