Have you tryed lowering the t.v pressure?If you turn the line pressure up it gets sensitive on the down shifts(floods worn circuts)
Also a worn t.v bore can cause this problem.
Did you use the trans go kit in you a500?
I believe they design and test there kits when the transmission is new and there is no wear.When you jack up the line pressure the it ends up in places it don"t need to be.
I have reamed many t.v bores with shift problems,it works well in most cases.
Glad to see you got it up and going,once you take the voodoo out of the install many will follow.
Good work!!