If you don't have a load (towing), try 70 psi in all 4 tires. Sometimes an uprating will bite you because of the higher pressures. The truck may not have enough weight to form the proper tire shape.
This is referred to as 'ballooning' Picture running around on 4 inner tubes and what that would feel like.
If that is your problem, the tires can be ultra-sensitive to road defects and cornering can be uneven/unsteady.
I haven't found a good way to find this problem other than driving. My buddy has a tire shop. We pulled the wheels, rebalanced them (barely any adjustment, but did it from scratch), cleaned and thoroughly inspected wheel assemblies, suspension, etc.
I inspected the tire profile both with and without loading (on a rack or with vehicle's weight, not talking cargo or trailer), and whatever else I could imagine.
No change, nothing found. So we mounted the new fronts (different brand, but same profile and 10ply also) to match up with rears and viola! I can again take a corner quite comfortably on uneven road at 80mph or more. I only stress test that way, I don't drive like that ;)
BTW, this would be at 70psi unloaded. The sidewalls are so much stiffermthan the original P-rated tires, they do not suffer from the overheat/risk that underinflated tires do.
I may go to 72psi all around, as it would be within 10% of max inflation, especially when under load for safety reasons.
