650NutKase

I do the same type of hauling semi regular. I race NHRA Motorcycle. The 5k interval is fine.

BEHR91

I always go 5000k or 7500 or longer with full synthetic unless your using the truck hard like it is hooked to a trailer everyday.

650NutKase

The timing components in the 5.4 3v don't like extended drain intervals. The real issue with running longer than 5k isn't really how dirty the oil gets, but varnish. Varnish will make the VCT's stick and will eventually lead to the dreaded phaser tick. If you do go for a longer drain, make sure you have an oil that has a low NOACK %. These oils will be more expensive, hence the reason I change mine at 5k with any oil I use. It also gives me an excuse to look under the truck and make sure everything is tip top. (All this is assuming you have the 5.4)