3.55s in the Bullitt..

I would skip the 3.55's, they won't be worth it and you won't feel any real gain. Don't look past 3.73's even for hiway driving. I saw another post on here that with 4.10's at 75mph he was only turning 2750rpm. 3.73's will be even lower than that, which I think is very tolerable for hiway driving.

For your speedo you will either need to get a Speedcal ($150) or a custom chip ($250).

EMA's right. 3.55's just aren't different enough to spend the money on.
i'm not doing any racing so stock gears are good enough for my taste!

Thanks you guys, I appreciate your advice. I don't plan to do any drag racing, but was looking for a little more performance. (I will forget about gears.) I just installed a K&N filter, and a Hypertech 160 stat. Now I am waiting for my Breathless Performace fan switch.

Are there any other mods I should consider without going crazy? I do not want to touch the exhaust though. Any suggestions would be appreciated.

Thanks

since the exhaust is out of the question, I'd probably look next at an underdrive crank pulley and a timing adjuster. These are both reasonably priced mods that might net you 15rwhp combined. Good bang for buck.

I would also consider selling the K&N and get the Densecharger instead. Many members on this site have been very happy with it.