You should be able to spin it by hand when cold, the book says it should stop within 5 revolutions.
To test hot, there is a procedure in the book. In a nutshell.
Insert a thermometer in the shroud between the radiator and fan, drill a hole for it. If you block off the air with a piece of cardboard and start the truck. Run it at 2400 rpm and within 10 minutes the fan should start to engage, and get very loud. The air temp should be between 190 and 205. Then, remove the cardboard. When the air temp is between 135 and 175 you should hear a definite decrease in noise.
FYI, aftermarket fan clutches suck. Lots of people have problems with them.