highway speeds

(TLDR) Are the differences negligible at real world highway speeds (65 -85 MPH)? Would you even given the difference a second thought? Or should I give more thought to the higher speed rated tire if my use case will be for tires that travels at higher speed more often than off road? I'm...

This issue is recent and I need to figure it if one of my solenoid valves is sticking or something. Conditions: pics taken during highway speeds. Over Drive is active, meaning the 80 is hitting 4th gear on the hwy. Turning the OD button off/on make the RPMs jump another 500rpm. Engine is...