[Backtobasics]

I am surprised no one has spoken of an under belly pan. There is a huge differential under the front end that catches a ton of wind.

Since it is 4wd and work based, I would look into a diamond tread or sheet metail belly pan / skid plate. I would also look at the area in front of the front wheels. Huge void, that are begging to be blocked off.
There is a lot of real estate under that truck. Skid plates would offer protection offroad, and smooth air flow.

Where is tire pressure? Many of the HD trucks have tires that can go as high as 80lbs.