Need help deciding between three different truck models

[Redland1]

Hello.I am trying to decide on a KW T800,T660,or Prostar.The truck will be used to haul frac sand with a hopper bottom at a gross of 80k.95 percent of the driving is highway and the last 5 is on oilfield lease roads but that have a maximum speed limit of 15MPH,so I think one would have to drive recklessly to tear one up on those roads.Also What speed on the transmission and gearing do y’all recommend for what I’ll be using it for? Roads are pretty flat with the occasional hill here and there but nothing crazy.