Well, my trailer puts my Silverado down to the stops when I put it on, so I also added some bags.
I run 80-90psi when fully loaded and less than 5psi without the trailer.
It will vary greatly on trailer size and tongue weight. And is it 1/2 ton, 3/4 ton, 1 ton, a pull behind or a 5th wheel?
The 3/4-1ton trucks don't need as much help.
Just be careful of over loading your truck. I have a friend who went through all this with the airbags and such, on a 1/2 ton, and he ended up rolling his truck with the toyhauler attached. Insurance wouldn't cover a dime of it because he was beyond the maximum load limit of the truck. It was a total loss of truck AND trailer. Just something to think about when pulling these trailers with pickups.
You can run between 5 and 100 when empty if you have Firestone bags... I run around 20 empty and 55-65 loaded on my 1/2 ton Ram pulling my 8K lb trailer... 5 psi is the minimum, to keep the bags from creasing which will eventurally lead to dry rot.