Mike,
The convertor seems a little tighter than 3500. I attributed that to the intake and cam not allowing it to make good torque. I hoped with the gear change it will loosen the convertor up by raising the RPM's.
If the convertor does truly work on torque...and this combo doesn't build much...if more torque was introduced wouldn't it stall a little higher?
That was the reasoning I used for an intake swap...
Originally I didn't want to do a gear change as I thought it was a band aid and I was just covering up the real fix.
I thought if I could make it run as good as possible with the 3.23's... then changed to the 3.91's it would be that much better.