I ran Continental tires that only lasted 30,000 miles and the Michelin LTX had much better wear than the previous. I went to 19.5" tires after that and have not worn out a set that has not aged out first.
How much weight is on the rear of your truck when you have the FW loaded and filled? I switched to 19.5's because I was loaded at 7500 lbs on the rear and did not feel confident in the load bearing of those tires even though they were labeled for more.