Just wanted to chime in that I daily drive my 54 4100. 235 with SM420 and 6.17 rear.
I will take on occasional long trips - even on the highway. Everything is stock, and everything is redone/gone over. Will cruise quite well at 45mph and I stick to roads/highways where that speed is legal. I will bounce up to 55 temporarily to handle "situations". I've had stovebolt 6's in boats for a long time, and cruise is 2/3 max rpm. So I follow the same rule with the truck - with the tires I have it puts my normal cruise speed around 45 on the low end and 52 on the high end.
She does get used to haul stone, mulch, top soil and firewood - has working dump. Primarily used for groceries every week. Gas mileage is about 10 when I run to the next state.
I have one kingpin needing attention, but she handles well and probably has the best brakes of anything I drive (fleet of 7 vehicles, 1931 thru 2015). I do go over the braking system weekly, and check master fluid level before each drive. I did have a modern dual master fail completely, so not worried about single cylinder master system.
I hate expansion joints on highways.....
