I'm betting you are shifting below your peak HP rpm. Have you tried taking it to 7400-7500?
I think there is more in it but I haven't started leaning on it yet. With a 30" slick and only 4.10's the car definitely wants more gear and RPM. I'm possibly changing the gear later this fall, I'll test first with a 28" tire and see how it likes that.
Only thing potentially holding it back up high would be the camshaft which is installed 5 degrees advanced at 103.