I think that exhaust is too big for the LN3. 2.25" is perfect up until power boosters come in [Nitrous, Supercharger, Turbocharger]. Did you get headers? Clean up that retarded thing at the end of the rear header [a poor construction lip] if factory headers. Tons of little things you can do. If you have a scantool, maybe you can find out more of what your ECU is doing, and perhaps tune to that chip real well, or maybe do a little bit of fuel work or spark advancement [93 octane tune].
Awesome track times, btw. What final drive ratio you running and what is your curb weight?