The problem with diagnosing clutch fan coupling is you can not always use the temp gauge for reference . The temp gauge is sensing coolant temps , not air temps. A bad thermostat will raise hell w/coolant temp, but the ambient air temp at the fan clutch will not even be close to coupling specs.
Same goes for a radiator with dirt/leaves, etc blockage between the rad and condenser . If these are blocking air flow , the clutch never sees this extreme heat at its sensor/pin.
The best way to check temps for a fan clutch is with a IR Temp meter pointed at the viscous sensor area. , not looking at a coolant temp gauge.
I would guess that the biggest mis-diagnosed part of the cooling system is replacing a viscous instead of a thermostat, along with no aux fan operation.