I run 80 in all 6. (Goodyear 19.5") The sidewall shows 85 or 90+...depending on the year of manufacture. Goodyear apparantly changed something in the manufacturing process, saying the weight of the motorhomes using the 19.5" tires has increased, so they are "answering the call" to to speak.
In years past, the state inspection, I found that when the vehicle was on the brake station...the weight was also recorded. By individual tire, by axle and by total weight. I asked if they would give me a printout, and they did. 3 times. (Now, of course, "inspection" consists solely of emmissions, so no longer can I get this printout.)
Anyway, I called Goodyear customer service once and read off the weights as shown. I told the person I am running 80 in all 6...and was advised that I could even run with LESS air pressure...but if I was comfortable at 80, leave it there. So that's where it remains.
I get 7.3 mpg towing and 7.8 mpg not towing. Chevy HHR= 3400# and the Ford Ranger=4000#. Been down to a low or 6.something and a high of 8.