I bought a truck with new virgin tires on the front/rear axle and worn tires on rear

I have found in one book that airing up the smaller doubles on one side of an axle 5psi more gives you a 5/16-inch difference in tire circumference

 

I think it's only a problem if you're driving around on dry pavement with the power divider locked for extended periods, which I have no idea why you'd do that anyway. In low traction situations the tires will scrub so easily that it shouldn't hurt anything.

 

Match em.

Virgin all around is what I would do. Once a year when the drives spun on first ice I would have shop get 8 new ones put on. Which worked out to 110-130K miles annually.

Tolerances are pretty close these days and they need to match, the tires all around back there.