The gauge uses info from the CHT sensor, which you state you have replaced! It's not right the bottom hose is cold, this shows the circulation not being what it should!

Normally if this is a problem you will notice running problems with the car and EML illuminated, being that it's a major input for the ECU to run the engine.

Use the cylinder head for your temperature testing (Not the plastic cam cover though)

The impellers are common for breaking up on the pump, due to them being plastic, just physically check the belt tension that drives the pump by hand.

Plus 108 degrees is way to hot, should be in the late 80s, early 90's ideally (The stat opens at 82 degrees)

Martin