I been shooting a Browning Gold for over 3 years now, I don't shoot 3 gun yet, and the guns been pretty much flawless unless I don't maintain the gun in any way for a few hundred rounds. I use it for hunting, sporting clays, and skeet.
Does the gun work without the mag extension? If it works fine without the extension, then it's obvious the extension is causing the problems. Maybe you can try the other mag extension that Brownells carries.