Check it out tomorrow and see if it reacts similar.
If it is, stop to idle for it to stabilize (but don't allow it to to stay hot for a long time). Shut it off and immediately spin the cooling fan. If the fan easily spins, the clutch mechanism is likely failing.
Are the fins of the radiator all mashed over? Is the grill/radiator blocked?
Next option would be water pump not circulating coolant properly.
Technically, 87 isn't all that hot. Especially for the highway, no excuse for a cooling system not to cool adequately on the highway. I'd first get the cooling system checked to ensure it's properly flowing coolant. The fan really doesn't do much on the highway.
If it is, stop to idle for it to stabilize (but don't allow it to to stay hot for a long time). Shut it off and immediately spin the cooling fan. If the fan easily spins, the clutch mechanism is likely failing.
Are the fins of the radiator all mashed over? Is the grill/radiator blocked?
Next option would be water pump not circulating coolant properly.
Technically, 87 isn't all that hot. Especially for the highway, no excuse for a cooling system not to cool adequately on the highway. I'd first get the cooling system checked to ensure it's properly flowing coolant. The fan really doesn't do much on the highway.