Need a reliable trans that will last

I currently have a broken 904 in my car. Not sure what happened. It might be something stupid, I just haven't actually dropped the pan to look. The fluid doesnt look or smell burnt, it looks brand new. Its a built 904 that I was told will handle 500 hp. After doing a burn out it broke.

What its doing: I put it in drive and it goes no where, if i rev it, it will rock maybe 1/2 an inch. If I put it into 1st, it will drive. But if i give it to much throttle it will just drive through 1st. Like its slipping. I have to manually shift it (on the column) into 2. If i put it from 1st then right to 3rd, it was go into second and upshift on its own into 3rd. It will also downshift on its own.

The car makes around 550 hp. Now, my question is... is it worth fixing this 904? Can it really handle what my car is making? Or should I go a different route? I take the car on the highway a lot so maybe something with overdrive?

Id like to keep it an auto. I defiantly Dont want a manual valve body but ive also always had issues with getting my lokar cable to shift perfect.

Thoughts on what I should do??