wat and then adjust them accroding to the track im racing on nd my top speed will return to its previous level?
I wouldnt say that about the top speed... but with the customizable transmission you can adjust the last two gears to make them quite long. That will restore, if not improve, the original top speed. I recommend that type of setting for courses like super speedway, test course and the Fuji Speedways. You get good low-gear acceleration and a good top speed as well.
But be warned - you have to strike a balance between top speed and acceleration. Its all good and well if you set a gear to its longest, but the acceleration of that gear would be crap. It might take ages for you to gain, say, 50mph. Similarly you set a gear to short, and you will gain speed really fast, but you gain not much speed. You barely make 50mph. So be careful.