EZ Dodge Cummins Questions

Good morning,

I am asking around on a few forums about a "new truck" that I am getting.

It is a 1989 Dodge 4x4 standard cab Cummins with a 5-speed.

My main intention is to use it for towing and hauling and occasional daily driving duty.

Assuming that I drive normal, 60 or under around here, what is a reasonable MPG to expect empty? Loaded with a 6k load on a trailer?

Best mods for mileage etc?

Also, I will likely limit any mods to exhaust and intake. I am most interested in keeping the mileage up. Not worried about racing it!

Thank you for any help.

ROB