Regarding tire pressure;
my race car hauler, A 1988 GMC crew cab Duallie, 2wd, 454 auto with 3.73 gears and no OD. 28 foot united express line trailer, 9000# GVW.total weight of truck/camper and trailer loaded, 19,000#.
Truck has a TBI motor, Edelbrock intake, no water heated base, has a vortex atomizer, Edelbrock stainless headers, 3" single exhaust, no cat, no air pump. 110,000 miles. Truck has had a pampered life. Never seen a snow flake. Turbo 400. Took me 5 years to find it. I race a nostalgia car, needed (wanted) an old body style truck. Same body style as a 1973-up.
Back to the nuts and bolts of what I found setting this thing up.
1)Tires call for 65 on both truck and trailer. Gets less than 5 mpg this way, more like mid 4s. Worse at 55mph than 66 mph with any pressure. Tires run over 125 degrees. Engine runs a 220. It's gutless too. no timing, tons of fuel with that eng. temp. We read the prom, can't seem to change it though.
2) Remove all antifreeze and run 2 bottles of Redline Water Wetter, it goes up to 6.5mpg, 190 degrees, lots of power. Still has a lot of rolling resistance.
3) I put the trailer tires at 75#and the truck at 90# rear and 80# front...gets 7.5- 8+ mpg. Tires run less that 115 degrees on the hottest day. lots of power and it rolls down the road with little effort. Still gets better mileage at 66 than 55. Those speed restricted highways in Illinois kill my mileage. It hates 55, it lugs the motor too much and sucks gas.
I have two tanks and I check mileage and tire temp at every stop, every time. This info is solid and has been verified over a 40,000 mile span of hauling my race car with this set up. May finally need front tires this year, have some feathering. Rears are 70%. Been on there for 14 years. Tires Always covered outside when sitting, stored in climate controlled building.
That's my story and I'm stickin' to it.