Walmart will not install tires that your vehicle was not "designed" for (ie. the sticker on your door). So unless the sticker says 31x10.5x15, which I doubt, you'll have to get em installed elsewhere. I tried getting them to put on 235/75/15s on my jeep and they said nope, sticker says 215 or 225.. eventhough they fit just fine and it's fairly common to run oversize tires.
The ATs that consistently get best reviews are the Bridgestone Dueler A/T Revos, but they aren't the cheapest tire.