Does the truck have a tachometer in the dash? If so what is the redline show for it? I pull hills at 4,500 in the Suburban with an old Chevy 350 and is does fine. As others have posted gasoline engines like to rev, It's the diesels that redline at low RPMs.
As to the 65 mph rating, we are talking about the ST tires on the trailer, not the truck. I would be be careful to not over speed the trailer tires. They all seem to be cheap junk that self destructs and tears out the underside of the wheel wells and plumbing when they let go.