I've got a weird problem with my 99 Cobra that maybe someone here has some insight on.

It runs around 150 degrees when driving down the street at any speed over 60kph.
Even colder when the weather is really cold.

In town at slow speeds it will come up to 180, never overheats, fan comes on around 185-190.
Once fully warmed up, runs great.

At 150 degrees, it will hesitate as I roll into the throttle and feels down on power- probably as designed due to programming - it never gets out of the warm up section of the map.

I replaced the thermostat with a brand new OE Motorcraft one, exact same result.
Anyone ever seen this?
All i can find are posts about these cars overheating.