I'm looking at getting my first truck. Is this a good set up?

I'm looking at getting my first truck. I'll be pulling SB through the mountains.

The truck I found has series 60 515, 18 speed and 3.73 gears.

Is this a good unit to pull the mountains? What kind of mileage can I expect? What RPM's does the engine like?

I've never ran a Detroit. Thanks in advance.