I had this happen on mine, and checked the freon level with a walmart freon kit gauge, and it said it was fine. It started to blow cold out of both vents after that, then the amount of air that was coming out of the vents was minimal. I pulled the fan motor (passenger side floor board, 3 screws) and felt up in there; and the recirculation door was blocking the air flow. I pulled this out through the fan opening, and have not had any issues since. This maybe something that may assist you.
2003 3500 2WD, DRW, Quad Cab, 48RE, 3.73. stock HO. Dipricol Tranny, Boost, EGT Gauges, Firestone Ride-Rites
Jeff K. - ACDC