There are plenty of gas vs. diesel threads for you to read, but I will just add this: I'm currently loaded at 20K GCWR on our Seattle to Barstow trip. Although I feel I could do this in a gasoline big block powered rig, it has been a very comfortable drive with my diesel. This comfort and quiet while driving just makes the trip that much more enjoyable rather hearing the gasoline engine spool up RPM's to make Tehachapi and Siskiyou Passes. I am spinning 2500-2800 RPM on the passes and 1500-2200 RPM on the flats depending on speed and headwinds.