Making the most of what I've got

[KiltedBanshees93GT]

The reason for this question is that the other night I got into it with a Nissan SUV, and barely held my own. (Granted , when things started I was already too high in the power band)
Anyway, my question is why doesent the car make more power (seat of the pants pull. She doesent even brake traction i.e. spin from a stop) Is there something flawed with my combo? Or does the car just need tuning? (she does have a new carb, which I'm still learning. The old one was way rich, but she could chirp second w/ the shift kit the new one is a lot smoother, but no chirp)
Currently she has a holley 4160 vac secondary (if anything tuned a bit lean), 66 shelby Hi rise manifold (too much of a high RPM manifold for the app?) Unknown heads, possibly stock and hooker tri-y's. This is on a 289 w/ about 60k miles.
What areas should I focus on to make more streetable power?
Also, is there any way other than via the eardrum to see what my cars preferred rpm is? She seems to have some good pull on top, but the 3 speed drags it back down, and I dont want to risk blowing my motor or tranny trying to pull it up high.

Thanks,
J

P.s. the tranny is a c-4 w/ shift kit, and the rear is a 3.25 posi. (looking to go for a 3.73ish ratio in the future)
I can't wait until I get a t-5 into her......