that truck looks familiar bro. where did you get it? if i were you bro, i would pull the valves off and clean them up. that is really what it sounds like. also check to see if there is a water seperator between the compressors and the tank, if not you should invest in them, they aren't that bad. hit up my boy Dev at
www.thebagshack.net also, check to see if there is a drain cock on the bottom of the tank. if so crack it open and see if there is any water in the system. that can cause problems with the valves. hope this helps bro.