it could be the hammer or sear is overly worn, this can cause it to skip shots and is quite common with spyder type guns
if you take the internals out you should see the hammer in the bottom tube, it's a small metal or sometimes plastic part with a single o ring on it, just make sure the o ring is in good nick and that the hammer itself isn't worn (also check that there is a rubber washer on the spring behind the hammer) if this washer is missing then the sping might bind during cycling and cause problems
and the sear is sticking out of the top of the grip frame when you take it off and should moove smoothly when the trigger is pulled, the sear could be worn or rounded
hope this helps
Ryan, team domination