Dallas, Craig has answered the question pretty good, and I will add:

There is a "TPC" spec on tires. This relates to how much money the OEM wants to spend on outfitting their vehicles. It's a long story to get into but, I found it relates to the warranty period. If a new truck comes with 50,000 mile warranty, the OEM tires will last less. If you watch these guys from year to year, and they put a 100,000 mile warranty on the same vehicle you will notice they change the rubber and the tires last longer.

How did I do it with my tires? My OEM Goodyears made it 70,000 miles and I don't speed, don't punch it from every red light, I'm not hard on the brakes, and I have all open road and no city to deal with. Most sets of tires I get 60,000 or so.

I pulled a set of Michelin LTX's off of my new '02 2500 Diesel and put them on my 1/2 ton work truck (different truck than above): they went over 100,000 miles.

With that little experiment, instead of putting on "P" tires, I went with a 3/4 ton spec tire. "E's" or something like that, I'd have to go out and look at them to be sure. And, this seems to be working, so I'm going to keep it up.

I paid dearly for them though. When they first came out I think they were close to $380 a tire (285's) mounted, balanced and tax. One of these tires is going to get hung on my garage wall with the final mileage written on it.

No doubt about it, I'm getting another set before Michelin discontinues them.