4.10 vs 3.55

[82F100SWB]

What I found with my IDI, keeping it at or a little above 2500 rpm while towing, there was never an issue with pulling a hill, mind you I was also pushing 13-14 psi at said rpm under load, so, it was making pretty good power too. Oddly enough, even spinning 2500 all the time, the thing still got good mileage.
However, any IH application I have driven with an IDI generally runs 24-2500 rpm at it's designed cruise speed. I'm thinking there's a reason for that.

 

[david85]

For actual towing, I've had good results with 2300 RPM, EGTs at 600, and boost up to 5 psi. Power and economy are acceptable. The tall gears I have are ideal for cruising empty. I can't tow much in 4th.

It really depends on what you use the truck for. I need to cover long distances on highways that I would get run over on if I was at a mere 65 MPH. Since this is also a work vehicle and not a toy, fuel economy does matter for me and I'm not always moving a lot of weight. Others may not need to cruise that fast or that far.