Depends on the weight/size of the truck.
If it is a 2 ton then you will need higher RPM to keep it moving.
If it is a 1/2 ton then I think about 2,100 - 2,200 rpm is ideal for a 235.

I put about 8,000 miles on my 235 in a 1 ton, all in about a month, kept it mostly at 2,450 or so, but would have run it a tad lower if I had the gears, I was limited to about 55 as it was.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-