2002 7.3L in a 33ft 15,000lb motorhome RV

[beancounter]

I am negotiating to purchase a 1989 Spectrum 2000 33ft 15,000lb motorhome (RV) with a 4.5:1 drive ratio. The power options offered are:


1989 460 V8 with 3 spd automatic Tranny

2002, 2003, 0r 2004 6.8L V10 Triton with a 4R100 Automatic Tranny

or either a

2002 7.3L Power Stroke Diesel with 4R100 Automatic Tranny


I have been told that all of these options will operate in the ranged of 2000 to 3000 RPM around 70 MPH.


I am concerned about power in the mountains of NM and CO.


What is the best combination?


All advice appreciated.


Thanks,
Beancounter
San Antonio, TX