With the old thermostat, temperature at the housing was sometimes in the 190s and sometimes in the 170s.
After a few more tests, if it turns out the new stat is actually a 201 degree-er, is that a fatal flaw?

 

Typically when it's the sensor, you will have several other codes because the ecm isn't getting the correct temp, causing driveability issues such as bucking, hard to start when engine is at operating temp, etc.

 

You live in TX? Then the 201 might be too hot for the next spring/summer. Try looking up what the manufacturer recommends for the warmer areas.