Ran them right at 40 psi on my 1500
I looked up a Load Inflation Table to determine what pressure was needed.
Stock Goodyear’s are only rated for 2,365 lbs max.
When a P-metric tire is installed on a light truck ( SUV, pickup, or minivan) the load capacity of the tire is reduced by a factor of 1.10 as prescribed by the Federal Motor Vehicle Safety Standards.
Stock Goodyear is 2601 lbs @ 44 psi so 2601/1.10 = 2,365.
Now having this info I looked up the 285/65/20 in the load Inflation Table and found that the 285/65/20 @ 40 psi is rated for 2390 which is sufficient as it slightly exceeds the stock tire maximum capacity.
If you really want split hairs, the 285/65/20 is rated for 2,369 lbs @ 39.5 psi.
Here is a link to a Load Inflation Table. I have a printed copy, good to have handy:
https://toyo-arhxo0vh6d1oh9i0c.stac...ication_of_load_inflation_tables_20170203.pdf