Did you try to shift it higher or lower? did you dyno it? What do you shift it at? What does the converter fall back to when you shift it?

http://youtu.be/RTDkU8WCjLo

70 Duster W8 motor.
1.29 60ft 5.79 1/8 at 120 mph
glide with 1.80 gear
@3170 lbs.