The maintenance schedule says to do it with every oil change - 5,000 miles.
For soft tires, that's necessary to try to make them last longer. Soft tires have better dry traction (making them "performance tires"), but they only last 20,000 to 30,000 miles.
Personally, I think that's overkill for harder tires. The Michelin CT's are rated at 65,000 miles. For something like that, I'd say 7,500 miles is often enough.
It certainly doesn't hurt anything to rotate them more often. If you have your oil changed at a dealer and they throw in a rotation for free or a couple of bucks, you might as well do it while you're there and they've got the truck on the lift.