In my opinion...
If you want an M715 you want lower highway speeds, bottom end gearing.....brute force.....
If ya want a factory type pickup that looks like an M715, put the cab and bed on their frame....
Then theres that "other world"...modify the M715 with new drivetrain components but do it in a way that gives you low gears AND highway speeds higher than stock AND upgrade the surrounding systems to be up to the task....
Ideally for me, the first and the 3rd above....one of each, would be my choices...and so thats my goal...yours will vary I'm sure!!
brute4