You can get a PA (Performance Automatic) full auto valve body. I believe that this will allow manual shifts??
And on the stall settings/j-mod settings:
I have the 300hp drill spec in my junk 95 right now, and with the stock converter, and good stock size tires, it will pull the rears loose on dry pavement a bit when it goes from 1-2. I could care less about how hard it shifts, as long as it doesn't shift so hard that it gets out of control if my wife is driving it around. She's not what I would consider "skilled" in that area.
I think what I'll end up doing is: 450hp J-mod, 2800 stall conv., no springs? (I thought the 1-2 piston required at least the top one???)
If this thing shifts smoother than what I have now, I'll be upset to say the least.
These are highly engineered precision vehicles, the first step in diagnosing the problem is to strike the suspected offending part sharply and repeatedly with a blunt object, then re-test.