Seems like your truck will tell you where it's happiest at. For me the 235 likes around 2800 - 3000 RPM at cruising speed. Any less and it feels like it's lugging, any more and it feels like it's wound a little tight. You need to consider your gearing and any load as well. I have changed the rear gear on my '58 1.5 ton to a 4.88 (from a 6.17) and added a 0.73 overdrive (NV4500). I shift around 3000 - 3200 RPM. The Truck will do 65 MPH or better but feels comfortable at 60 - 63 MPH, that's close to 3000 RPM in overdrive..
