Ac compressor works but not cold

Your problem is it's a prostar, it will start working in a couple days...

Just kidding but my prostar do that and my buddy having the same issue with his prostar as well, it will work fine then one day out of nowhere it just stop working, then one day it start back working again.
Check to make sure you do not have too much freon in the system, also makesure you have enough

 

Few things. Your Prostar will have lazy ac temps for two reasons. First, your main cab air filter, if it's dirty, it restricts flow over the evaporator. Second, the lower kick panel in front of the passenger seat is actually the lower blower box cover. It is very easy to mis-align this panel to the slots when reinstalling it causing warm cab air to be sucked in and around the evaporator instead of going through it. So have a good look at it and make sure it is installed properly.
After that, I highly recommend having someone with Diamond Logic builder connect to your truck to see what the ac temps and pressures are doing. Taking resistance readings at the thermistors is fine, but that doesn't show the whole picture in case the wiring is bad somewhere else and the body controller isn't seeing proper values. Connecting an ac machine and checking the charge is also a good idea to make sure it is also proper. 3 pounds with a sleeper, 2.5 with a day cab.