After all my haggling and checking, Costco can sell me 4 of the Michelin XDS2 245/70R19.5 for $1675 but can't mount them. That'll cost me about $100 to $150 more, so $1775 total.
Les Schwab will sell me a set of Toyo M608Z 245/70R19.5 for $1775 and that includes the mounting and balancing.
The Toyo is 'only' rated at 4540 pounds max per tire. However, for $9 a tire more, I can get the 265's which are rated at 5510 pounds max per tire. My wheels will be fine for either, but actually more in the middle of the range with the 265's over the 245's.
Now, I know the 265's are taller; an inch bigger diameter so a ride of 1/2" taller. I have a 2" leveling kit on the front of the truck and have run that diameter tire in a 315/70R17 BFGoodrich T/A All Terrain.
That works out to 3.6% less revs per mile for the 265's over the 245's. I don't think that's a problem with my drivetrain.
So, for just a hair over $1800 I'm going with the 265/70R19.5 Toyo M608Z from Les Schwab.