Low Refrigerant is likely the problem, and certainly the easiest to try to fix first! Because of the position of the condenser in the truck, the passenger side of the truck is cooled by the upper portion of the condenser. When the refrigerant is low, that portion doesn't get as much refrigerant, so the air running over it gets less cold.
As an FYI: I just tried to fix the same problem with one of those "do it yourself" kits from O'Reilly. Paid $50. It didn't even get close to high enough pressure to overcome the pressure of the refrigerant that was still in the system. Luckily, I returned it, and they took it back. I do like that place. Took it to a pro where they flushed the whole system and put in new refrigerant. Cost $100. 00. Works like a charm...