The advice that Headbasket above is exactly what I found
with my 2000 E450 24' Class C.
I had the brake system redone by a local independent truck center that opened it's shop in 1970. The owner checked everything and said I overinflated the tires at 80 PSI. He adjusted them downwards. Perfect handling after that.
I contacted the tire manufacturer and they advised that without a 4 corner scale weight, they would not recommend any tire PSI settings. I still have to do that.
The problem was the tire only had a center footprint and not the whole tread
making contact.
So far 72 PSi has worked well on the front.