Yeah, cleaning the barrel is always a good plan. Also you might have grease on the hop rubber, so if cleaning the barrel doesn't help maybe break it down and use a cotton bud and rubbing alcohol (isopropyl) to clean the inside. Make sure to give it a quick wipe with a dry bud because most isopropanol has a bit of water in it which will not evaporate. You could use soapy water instead, but rinsing and drying would be more of a pain in the arse.
Just to check what you mean exactly though, what sort of range do you mean, in meters? Because although TM guns get good range at 280-300FPS, most guns don't.