I noticed the same thing when I suped up my PT Cruiser (bad first car choice, I know). As mentioned above, get the full racing transmission so you can fool around with the gear ratios. Just in case you don't know, by setting the ratios wide, you'll get a higher top speed but slower acceleration, whereas setting them narrow gives you the reverse (fast acceleration, lower top speed). When I tricked out the Cruiser with all the weight reductions and other options, tweaking the gear ratios brought my top speed up from 127mph to about 170mph (if I remember correctly). Hope this helps.