There is a speed limit in Montana.
Kicked in back in the late 90s IIRC.
Interstates are 65 mph for trucks and 75 for cars, pickups, bikes etc. (they will give you 80-82 at times but I stick to 79).
State highways are at 60 daytime for trucks and 70 for the rest of us (60 for cars at night, 55 for trucks I think).
Feds forced the state to knuckle under by threat of withholding highway funds.
Wyoming has some stretches of 85 mph....FREEDOM!!!