13.9 is very respectable for a fully optioned non blown saleen with your mods. Btw, what was your sixty foot time, cause i can drop a 1.9 in my 99 which is mainly setup for open track events. If yours is any bit over 2.1 there is more left in your car.
Did you take things out like the spare, and all the other loose crap that doesnt need to be there. I used to be all hardcore into trying to lower my times, but i have stopped drag racing all together. There are plenty of tricks probably still left if you are interested in lowering those times.