Man you're maiking me sorry I ever let that bad boy go....

Think about it, you have the power to go high tens EASILY, you just got to get it to the ground and not frag the drivetrain in doing it. If your trans is letting go gradually it's been holding you back way before then.

On my motor I had an 833 4 speed and a 3.54 Dana so I wasnt worried much about tearing the drivetrain apart....I was much more concerned about buckling the quarter panel/roof welds out of my recently restored 70 Charger R/T

Get a fresh trans and put some real slicks on it and see what it does.