The game starts up fine, but in game I can only move ahead 1 inch by holding down W and have to mash it just to walk forward. How do I fix this?

Same problem here

mmm, months ago i read about this problem (never experienced) and a guy who resolved it using a joystick! hope it helps.

I've never experienced that problem in this game, but the joystick suggestion may hint at an answer. Do you have any other input devices connected, which might conflict with the keyboard or mouse commands? I had similar problems in Grand Theft Auto: San Andreas, which went away if I unplugged my joystick.

'course, if you don't have any such devices connected, I wot not what the problem could be.