rock solid man, those are impressive times regardless of how experienced you are. As far as getting them down more, there are a billion threads but like silver said, 373s out back will help you out big time, several tenths lower at least. Aside from that, for 200 more dollars you can put underdrive pulleys and a cold air induction system which together will get you another 15-25 horse and you can do both installs yourself in about 2 hours total.
to give you a breakdown, $160 for 373s, $10 for the correct speedo gear (the white one), $200 for the install of the gears, $80 or so for cold air inuction, and $110 for aluminum underdrive pulleys and you'll be flirting with that high 13 - low 14 mark. And thats if you get it all new, you can usually Ebay or shop Stangnet's classifieds for much lower prices on used stuff.
Add some slicks and you'll be in the 13s.