AC not cold anymore

With the truck running and a/c on check to see if the clutch on the front of the a/c compressor is turning. If so, then you likely have a leak and need to connect a set of gauges to read the pressures. If the clutch is not turning then the system is low or out of refrigerant or there is an electrical problem.

 

Just add some freon

 

Most common cause is low freon.

 

The AC works on btu exchange. If you have bugs and other road debris in front, stuck to the condenser, you can not get rid of the heat, thus can not make things cold.
Wash the condenser out good with water, then see if that makes it cold.
If somewhat better, but still not what it used to be, your cabin filter could be clogged, and/or compromised allowing dust and other junk to accumulate on the evaporator, again, not allowing the fan to remove the cold from it before returning to the cycle.

 

cabin filter clogged