The best way to figure it out is the chalk method.
1) find a nice big flat level parking lot somewhere
2) make a chalk mark across the tread 90 deg to the sidewall, just a single line
3) drive the truck slowly across the parking lot (DON'T TURN THE FRONT WHEELS)
4) get out and check the chalk line for wear
- if the chalk mark is only worn in the middle, drop air pressure a lb or 2
- if the outside chalk line is gone, raise pressure
5) remark and repeat (take the same path and distance driven before) until the chalk is worn off ~ 60-75% in the middle of the tread
(make sure you remark each time.....you can't re-use the mark)
Ideally, you want all the tread to be making contact with the road, but if you can get all but the outer most tread blocks touching, you should be fine.
Doing this may not even be close to what the door panel says.
On my 97 3500 4x4 dually, to get a good chalk line test, I had to keep the fronts @ 65 psi (cummins), but the rears, I ran @ 25 psi each for all 4. If I remember right, the door said 65 psi
No weird tread wear or problems.
When I towed, I bumped the rear up to as much as 50 psi, depending on the load I was towing
