[91LX2Bfast]

E-town is one of the fastest tracks in the country, so the track is not a problem.
Your 60ft time definately shows that you have a 13 sec ride with some traction, but its not that horrible. You just have to practice a bit and you should be able to get that down to 2.1 and that alone should put your car in the 13.9 range. I like right around 27-28psi in the rear tires, and about 38 in the front. There is no point in going with any lower pressure in the rear with street tires.
The humidity could have hurt your car's power, but the temp was very cool, so i don't know why your MPH is still low. Have you performed a tune-up? It may need a set of fresh wires and plugs. These mod motors seem to need fresh plugs and wires about every 20-25K miles. What are your shift points?
The best advice to give you is to just practice. Practice your launch and get that 60ft time down. Also try to find your best shift points. Go back on a cool day with low humidity and see if your mph picks up. If it doesn't go at least 101mph, then I would start to look into reasons why your car isn't producing as much HP as it should be.
Just for comparison, my brother's auto '99 GT (260hp) with a chip, MAF, and X-pipe goes 14.1's@98.5 spinning hard in first gear. His car should be putting down about 40-50rwhp less then your car. That's why I say your MPH is very low for your power.