Ram 3500 here SRW with a camper sitting at GVWR. E rated Falken AT/3W in 37 x 12.5/17. Your rear axle max rear weight according to the MFR is 6,800 lbs., so 3,200 lbs rating/tire is needed. Per their inflation chart 45psi gets you to 3,250. I like to run things a bit higher, so I am at 50psi which they say is for 3,525lbs per tire or 7,050lbs rear axle weight. At their max inflation pressure of 65psi, they are rated for 3,970lbs per tire or 7,940lbs rear axle weight.
At 65 psi the ride would be a lot rougher, and in theory would wear out the middle of the tire carcass due to over inflation. Larger air cavity requires fewer PSI for the same load. Some weird voodoo witchcraft they call science and stuff. I just follow the tire load rating and inflation chart, and if given the choice pick a higher ply tire E vs. D if available for a bump in durability.