Incorrect Temperature Gauge

What would cause the temperature gauge to read off by so much? When my engine is fully warmed up, verified to be running around 190 degrees by a scanner, the gauge in my cluster will be only reading about 150 degrees ( the 2nd line on the left half of the gauge. I've replaced the temp sensor and the temp sending unit.

Scanner tempt reading could be off to.
Get the old or new type thermometer out and see what the real engine tempt is.
Did you change the tempt sensor for the gauge or the VCM?
Or the temp gauge in dash?

For as cheap as it is I would replace the thermostat and the gasket and possibly the rad pressure cap total of under $15 american and see if that changes anything.