Is my thermostat ok

The 160 deg thermostat is not helping the engine stay cool in the summer. Once it reaches 160, it just stays open. A 180 would help heat and to reduce wear in the winter without changing the summer cooling.
Getting warmer on the highway points to air flow problems. Adding an air dam under the radiator core and making sure the seals are around the radiator are first steps to take.

If you do change it, be sure to get the full flow type. This one is the brand and style I use if given a choice. The picture shows they are not the typical Stant design that can close under high rpm flow and pressure.
I do not think that the thermostat will change much in the summer (unless it is not opening fully at RPM), but your defroster and heater will work better this fall and winter and your oil will have less blow by water and unburned fuel in it.

Since you are going to have to drain at least some coolant, try adding some “water wetter”. It’s a surficant that helps with heat transfer. It has been helpful in tractors and cars for a very long time, and is not snake oil.
Did you check for air gaps around the radiator and look into a lower air dam already? If your water pump is good, the lower radiator hose is not collapsing, and ignition timing is not off, that’s the next reason for running hot on the highway.