40 - 45 mph in my truck with standard (1956) 3.9 rear is about 1800 rpm . A standard 235 1/2 ton should cruise easy at 60mph , it will go faster , but your mileage will go away
If you have too much noise , determine where it is coming from and fix that . I predict it may be a cheaper option .
Jerrys "pull the fan off" is a good way to isolate noise issues.
Consider taller tyres as a small gearing adjustment .
I agree with the brake comments .
