I bought an 02 Chevy g3500 4 window with a 6.5 v8 diesel in September. I’m bare bones roughin it this winter and plan to build out everything this summer.

Nothing major seems to be wrong with the engine. Minor oil leak, fuel filter probably needs changed. That’s about it as far as I can tell. But I’m no professional.

I am however wanting to take it cross country for 2-3 months in the fall. 10 mpg isn’t exactly what I want for a long distance rig. Still learning diesels. Is there anything a shop could do to bump the mpg up? Is there an engine I could have swapped that would make enough of a difference to be worth it? I want to keep this thing around for quite some time so I don’t mind dumping some money into it.