if trailer tires only good to 65mph, why not switch?

Based on experience, my truck surely can pull 75-80 MPH. See my signature.

BUT for every 5 MPH over 55, our MPG goes down 20%.

I run at 62, because I can't afford to run any faster.

For years I cursed RV's running below the speed limit and promised myself that when I retired, I would have a rig capable of traveling at whatever speed is posted.

I now have one, but chose not to run that fast. It is just too expensive, tire capability aside.