Are you going from 5th to 3rd on downshifts? I notice that you also don't bring it to redline on the straights, bring it to the line, you won't hurt it. You're making the most power in the higher rev range- use it to get higher speeds and flow that speed thought the turns. Your biggest gains are exiting oak tree and the last turn prior to the front straight. Use the redline and power of that most awesome motor to go faster.
I would say no lower than 3.5k on the tach while on track. You say you like to row your own, you will be busy. Stock diff? If so what is the ratio? Think about going to a 410 and using 6th gear on the back straight. Install that and you will be under 2 minutes for sure. Can you set up a camera so your hands,feet and head are showing?