Did you swap in that Cummins or was there a year that I wasn’t aware of it’s offering ?
To pull power I still think the Cummins is the “simplest”. The Ford engines are more complex than a BMW 7.
And yes, driving the rockies is incredibly demanding. Not even Colorado regulators seem to grasp this.
Ford put the 5.9 in the medium duty F600 & F700s. In the 90s.