BFG Ko2 tire pressure

What is the size and load rating for the stock tire?
On a 2nd/3rd Gen, 40 would be the adjusted psi for a 31x10.5R15LT.
There are a few reasons why you might consider it "high".
-you might have a light gvwr; 1st Gen were 4,250-5,100 gvwr...3rd Gen is 5,600 gvwr
-yours might be from a time period before P and metric tires were derated by 10% for use on trucks/suv...see Ford/Firestone fiasco

My, $.02 on chalk.
It is confirmation of nothing other than your latitudinal footprint; what's the longitudinal footprint look like? Modern radial tires don't deform the same as bias ply(usually LT flotation, agriculture tires) for which the chalk test was viable. Chalk, even if viable, would only be current weight; not possible weight(gvwr). Most of the popular sized LT tires in use on 2nd/3rd Gen lose/gain about 150 lb of load capacity per 1 psi x 4 tires. That's roughly a 8 psi swing between 'empty' and 'fully loaded'.

Most who use chalk, do not do it correctly. You're supposed to chalk, add 10%, and then equalize deflection by increasing pressure in the tires with lower deflection. This would be viable method for modern radial tires.

 

275/70/17's I usually run @36 PSI