I bought a used 5hp19 on ebay, they're pretty cheap. I will soon buy the controller directly from powertrain control solutions who is the company that actually makes it. pcs tcm-2000. They're very helpful and answered all my questions in detail.
Then you can think about rebuilding it with stronger parts. I don't think $4k is necessary but may be easier that way.
The only stronger aftermarket part I've heard of for the trans is the reverse drum, maybe they recently started building other parts, I don't know.
Advanced Automation actually told me NEVER to use this transmission with a v8 even after rebuilding it as it will only be destroyed, so it is odd to me that they would now promote it. I decided to do it on my own since they were completely against it no matter what the cost. In fact, 034motorsport told me the same thing. Too weak to handle a v8 even with our application. I figure the transmission isn't expensive so I'll give it a go + it's my only option.