Just for reference, my 1-ton came from the factory with a 216. By the time I got it, that had been replaced with a low pressure 235. That truck was originally geared for 3300RPM @60 MPH. The horsepower peak was also at 3300 RPM. I don't know it it would pull 60 MPH with the 216 but it would with the 235.
It now has a 261, whose stock rating was 150 HP @ 4000 RPM. I suppose the marketing department leaned on engineering to come up with that number because both engines are rated for peak torque at 2,000 RPM. I've re-geared mine with a 4.57:1 axle so at 60 I'm turning 2500 RPM in overdrive (17%). Crower cam has a peak torque at about 2800. I'll turn it 3600 to make the next gear but I don't run it that fast for long. What I've noticed it that the oil temperature starts to creep up at over about 2700. The engine is working hard all this time at about 10" vacuum on the flats and pulling a 3700 lb. camper.
A stock 235 has a torque peak at 2,000 RPM. Specific fuel consumption (gal/hp/hr) goes up pretty fast above the torque peak. So if you're running 3,000 RPM @55MPH down the highway, gas mileage won't be very good compared to say 2200 RPM @40MPH. I gained almost 20% in mileage with just a cam change that raised the torque peak.
