If you wanna help out your car at the high speeds, consider aerodynamics as your friend. A lower car will usually have less drag. Offensibly ridiculous wings will cause more drag with no benefit. Some body kits will provide better-than-stock drag, others will provide worse.
Since at those speeds you'll be in the higher end of your rev range, freer flowing components will probably help you out (I/H/E, maybe high flow cat).
But if it's due to the tranny/computer....then I'm not so sure any of this will make a difference.
Oh, and don't forget to kick out your 300 lb. girlfriend.
b