Before I towed my FW, I was at 70 all-around on my truck, since I wasn't towing or hauling anything serious. They hunted worse at the lower pressure and no weight. Also, I was running 80 as I had stuff in the bed of my truck, right up against the cab, as well as 4 adults and stuff =in= the cab. Tires are 265 vs the OEM 245.
Lyle
If your OEM wheels were 6.5" wide and then mount a tire with a 8" to 8.5" wide tread then hunting is a known issue with certain tire tread types.
I had a '90 2500 chevy that came with LT245/75-16 E tires and the skinny 6.5 oem steel wheels. I moved up a LT265/75 tire and had to have the tire dealer remove them . They hunted at any speed or psi.
He suggested LT235/85 with the same tread on those skinny wheels. The truck drove like it was on rails at any pressures.