Tire Inflation Question

I have the same tire and wheel size as you on my chassis when it was new in 03. My manual said to inflate the tires to 85 psi rear and 90 psi front. These tire pressures did not work for me due to rear tire squirm. I was also worried about heat build up inside the tire at 85 psi. I experimented with different pressures every time that I went out on a RV trip. I ended up using 100 psi all around. I get a slightly rougher ride at 100 psi (compared to 85 psi) but, 100 psi eliminated the rear tire squirm, eliminated the heat build up inside the tire casing at and, at 100 psi my tires get exceptional road wear (I ended up getting 10 years out of those tires @ 100 psi), I'm now into the 2nd year, on my second set of XRV's at 100 psi. Good Luck in whatever works for you!