Not building heat

Have you checked it with a back up tester like a water thermometer or an IR gun?
Have you tested the rad temperature?
The stat sets the minimum water temperature, so it's job is to stay CLOSED until it's calibration point. It doesn't care about the rad or the clutch. But it does care about the heater core.
If your heater is blowing hot, and set on full-bore, it is extracting a lotta heat.
With the stat closed, the hot water from the intake manifold is sent thru the bypass hose and back into the pump. So the heated water is going round for another trip. Eventually the water gets hot enough to open the stat, and most of the hot water goes to the rad, then the pump starts pulling in the cold water. If the water temp falls below the stat's set point, it begins to close again. And so it continues.

The only ways to make the engine run hotter, than the set point are:
1) make it work harder
2) retard the ignition timing
3) lean it out (make sure the choke is coming off)
4) Change the coolant medium
5) slow the pump down
6) put a parka on it