Okay, there are two possibilities:
- firstly, there may be a function in the game to configure the pedals - go there and set it up so you can acheive full braking and acceleration. I don't know the game at all, so this is a bit speculative.
- secondly, download the Wingman software from the Logitech website, and configure the wheel through that. I have the original GT3 wheel (which is just a Formula Force in a nice blue dress) and run most of my PC racing games through that. You should also be able to do this through Windows itself, but the Wingman software lets you tailor the Force Feedback effects a lot more thoroughly.
Good luck!