Have you pulled the trigger to release the slide? Is the take down lever installed back in the right position with the groove facing the grip of the gun, not the flat part of it or is it pulled all the way down enough to release the slide? I can't think of what else could be hanging the slide up during field stripping, if the trigger was installed right and everything else was put back in right other than the take down lever position or the trigger itself not releasing the slide. Are you trying to field strip it with the magazine in the gun? Remove it if so, I'm just throwing stuff out their to see if it helps you.