OK have you cleaned the gun barrel? Have you used a measured range to set the hop for optimum range with the weight of BBs you are using? Also what BBs are you using I generally find 0.28g are best for stockist guns. I would recommend changing the hop rubber (they do wear out over time), maybe get a better quality 6.03 barrel (I rate sticking with brass). See what improvements you get. Next would be to open up the gearbox clean, re-shim, regressed and replace o rings. If anything is worn out. If one gear is gone replace all other sticking with the same brand.