How much mud and off-road time is the truck going to see vs how much road time?
If it's mostly used on the road, you might be better off with a really aggressive AT tire instead of a mud tire, since mud tires tend to wear out relatively quickly when run on the street all the time.
I shod my Ranger with Sport King ATs the last time around and while not a mud tire, they did pretty darn good under any condition... and surprised me with how well they went under muddy conditions. They only lasted around 35-40k miles, but that's more than most mud tires and I think a pretty good number for an AT tire.
If its mainly mud use or you have money to burn, get some Super Swampers... pretty much any design other than the thornbirds, aka thornturd.
SSRs are reported to last long but you better have deep pockets. LTBs are cheap, limited selection, bias ply, but they really sling the mud and hold up decent. Boggers are serious mud tires....even when nearly bald. TSLs work pretty good too. I've heard mixed reports on the other designs.