My Samsung LN52A750 has gaming motion lag. Please help?

My tv has been acting odd while playing xbox 360, i have tried turning the tv to game mode, turning the hz 120 motion to off and high, using the black single hdmi cord from the back of the tv to the xbox, and have tried using the hdmi cords that come with the xbox. All of these things have failed to fix the problem. This makes playing first person shooter that require fast reactions or precise shootings hard and unenjoyable to play. All my friends cant play on the tv because the lag is really odd to them. It's hard to look around in small amounts, i barely tap the right joystick and it goes 2x as far as it should. ( no matter what sensitivity) Please help!