Something isn't setup right in gamefuel if your seeing a change after you turn it off. Make sure the Primary and 2ndary DNS IP addresses are filled in the Basic/Internet/Manual. DNS relay should be on.
I would run thru the gaming fuel sticky and for now, disregard the gaming and game fuel. Make sure you have static IPs on everything. Do some testing. If you see good speeds then go back and enable the game fuel and just add one Play station. Again, don't any any other devices like PCs, there not needed in gamefuel, just the PS devices. What FW is currently loaded right now on the 4500?