Lg Flatron e2041 Refresh rate and Resolution problems

Monitor: Lg Flatron e2041
native resolution: 1600x900



so i got this monitor after playing on a crt monitor for my entire life and noticed only a small almost insignificant amount of input lag but was so happy to have a widescreen monitor i put up with it. recently, while messing with some settings in catalyst control center i noticed that i could turn the monitor to 75 htz refresh rate and that when i did so it seemed that the hint of input lag disappeared and everything looked smoother at the cost of my resolution looking grainier and the auto adjust thingy(no other options to adjust video options on the monitor) always shifting the monitor half an inch or so off center. iv even tried all the resolutions i can, and the only one that seems to work is 1200x800 but i would like to get 1600x900 to work.

tl;dr how do i get this monitor to work at 1600x900 and a 75htz refresh rate?