How is your car off the line now? Feels heavy? Have you gotten any 60' times at the track?
I had 4.10s and 4200 stall in my 4th gen V6 daily for 2y. I would get the stall first and see how it feels. 5th gen trans is already much higher geared in 1st then 4L60E.
2000 Z28 - current daily
1996 Camaro 3.8 - previous daily