As the title state the fan on my engine never stops, unless the car is off. It is immediately on when i start it cold and stays on non-stop. When should the fan be running? I just replaced the fan clutch and thermostat what else could it be?

 

It will always turn due to parasitic drag in the clutch, but it should only lock up (match engine RPM) when the clutch gets hot (specifically the coil on the front of the clutch).

 

How can i tell if it is stuck engaged and matching the engines RPMs?

 

With the engine off and cold, try to turn the fan. If it spins somewhat freely (should get at least one revolution when spun by hand), then the clutch is disengaged. Now, get the truck up to operating temperature (radiator included so you may have to drive it for 20-30 minutes depending on your outside temps) to get the fan to engage. Shut it down and try to turn it now. There should be resistance due to the fluid coupling locking in inside the clutch.