BFG rates that tire for max 3195 lb load at 65 psi. I clipped the appropriate line from BFG's specs (see below). I wasn't able to find their inflation tables, which would give a good range, but here's a rough guide: Typically dropping the load by 10% would result in a recommended inflation level drop of about 10 psi, for tires in this general range.
Ram recommends 55 psi on the Toyos, and from the Toyo inflation/load tables, that means Ram is estimating a load value of 2900 lbs. That's about 300 lbs lower than the 3195 (3200) max that BFG rates the K02 for in this size. That's about a 10% drop in load. So it would seem appropriate to run them at about 55psi.
Now if you do find an actual BFG full load table that gives different loads and inflations for the same tire, you might get a more accurate recommendation, maybe 56 instead of 55, for example.