Runs hot at hwy speed cools down at idle, changed thermostat did not fix problem

does the cooling cut on and off? if is running all the time then that may cause loss of heat, is there any coolant loss?

Did you check the cooling fan?

my first thought is the themostat but I would also check to make sure the cooling fan is coming on when engine gets warm if not could be relays for cooling fan

Check first your coolant level. Start engine and turn on ac open hood see if cooling fans are running, if fans are running and coolant level is ok temperature should stay normal. If temperature rises squeeze coolant hose, it should be firm like you could feel pressure on the hose a sign that the water pump is good. Thermostat opens only when coolant reach normal operating temperature.

Have the radiator Roded

First, check coolant level. If okay, suspect themostat stuck open.

At idling speed an engine does build up a lot of heat and the cooling fan will kick in. In slow moving traffic or traffic jams the temperature gauge can touch the red - particularly on hot days. The reason it cools down when you start moving is because of the air flow through the radiator.

Presumably there are no leaks from the cooling system otherwise you would have mentioned it. In normal circumstances the fan will not be running as you are driving at speed, as the air-flow through the radiator is sufficient to cool things. The fan only kicks in to get rid of excess heat - and this usually occurs at idling speed or after you have parked the car.

If the fan is running all the time as you drive, this points to either a fault in the fan switch, or the car is running too hot. presumably in normal driving the fan isn't running and the temperature gauge reads normal?

It is common - in stationary traffic many cars overheat (particularly big engined models) try to stall and 'cut out'. Restarting can be difficult until the engine cools down.

Is your car overheating in normal driving conditions or just at idle speed? Overheating in normal driving conditions can be caused by things like a failing water pump, blocked radiator, collapsed hose, faulty thermostat or, in the worst case scenario, cylinder head problems.

Overheating at idling speed is 'common'. Check your coolant level. If your car isn't using/losing coolant then there probably is no major problem. You can flush out the cooling system and refill with new coolant - and also check your radiator. Are the cooling fins crumbling with age? Or maybe they're partly clogged with insects and debris from the road? A blast with a hosepipe wil sort that out ..

The question is how much does your car overheat in normal driving? If it doesn't .. it appears as though you have nothing to worry about as such. Most cars have 2 speed fans... the 2nd faster stage kicks in at some point dependant on engine temperature. Perfectly normal.

Your car should have a High and low speed connector there. That would cause the problem you described, if the PCM sees the temp at about 195 the low speed fan should kick on, if that fan doesn't provide enough airflow it kicks on to high speed to cool quicker. in your case the low speed is non existent and the computer is simply waiting for the temp to raise to the point where it triggers the high speed relay.

change your thermostat it may not be opening all the way

does it run hot while driving or in traffic?
if running hot at idle could be water pump not circulating enough try revving engine some and see if temp comes down. also check your fan clutch.
if running hot going down road probably radiator