If you do not have the bigger Clutch Drum that has more clutches I would get one. Do you use Kevlar Clutches when you build them (different opinions on them). Try to stay off the Power Brake Burnouts. If you need to get the engine RPM up on the line, get a bigger stall convertor.
If you want to sit and burn the tires use a line lock. As far as shifting, do you use a manual valve body or do you have your kickdown linkage?
Valve body and line pressure make a big difference on shifts. Be patient and watch for replies and advise here. There are a lot of really good tranny guys on hear. Way better than me!!!