My stock tires are a load range XL and I really want to get these dunlop mudders
http://www.tirerack.com/tires/tires....dial+Mud+Rover

But the load range of those new tires is C. Is that okay or should I find tires of the load range XL?

 

Actually they have a higher load range than what you have. You have a p series (passenger car) tire. Those are a LT (light truck) load range C tire.

 

Assuming you still have the stock size tire on the truck, the tires are rated for a hair over 2000lbs at max air pressure of 35lbs. If you get any tire larger and including the 10.50x31, they are rated for over 2200lbs. So yes, you can use these tires providing they are at least the 10.50x31 and larger. Fuel mileage will suffer and you'll lose some power due to the larger circumference. Your speedometer will also be off as you'll be moving faster than the speedo reads. I've found best mileage at max air pressure cold. They will also ride rougher than your current stock size. Make sure about the rim width before buying.

 

Labnerd you have been my savior lately, The 31's are roughly an inch or two larger in circumstance so I'm not too terribly worried about my speedo, I'm going to compare a gps and the speedo and run it at whatever speed it should be.
The stock rim width is i think 7 inches and I'm pretty sure i can fit up to a 10.5