1.)GO TO 'Documents\My Games\Gears of War for Windows\WarGame\Config"
2.)OPEN 'WarEngineUserSettings.ini" WITH A TEXT EDITOR.
3.)FIND THOSE TWO LINES:
USEVSYNC=
OneFrameGPULag=
SET 'USEVSYNC=" INTO TRUE, AND SET 'OneFrameGPULag=" INTO FALSE!

SO IT WILL LOOKS LIKE THIS:
USEVSYNC=TRUE
OneFrameGPULag=FALSE

THIS WILL FORCE THE GAME TO USE VERTICAL SINCHRONIZATION, BUT IT WILL COST YOU 10-30FPS FRAME/SECOND! SO STABLE 60FPS BECOMES LIKE 45FPS, SOMETIMES 30 FPS.
IF THIS IS NOT HELP, FORCE VSYNC IN YOUR GRAPHICS CARD PANEL, EVEN IF ITS ATI OR NVIDIA!

FOR MORE FPS, YOU CAN TURN OFF SOME GRAPHICS EFFECT WITH FALSE",-OR DISABLE D3D10.