Alero Trans issues

2004 Alero, 3.4, Auto.

So Ive searched this forum this but cant find anything that says "do this, it fixes it."

So heres the story. Girlfriend drives the car about 40 miles one way to work a day. About a week ago it started messing up at highway speeds, not downshifting correctly, unlocking the converter so it would rev up then clunk into gear. I changed fluid and filter, fluid was burnt up. Did fine for a couple days, now car wont go into reverse, and it seems like no first either because its very slow coming off a stop. Took it to a shop for them to read the codes and it came up with P0730, Gear ratio not recognized, but the thing is bone stock.

So jacked the car up again to check to see if I didn't fill it up quite to the top, and the level is fine but the fluid is burnt up again.

Does someone have an idea what the problem could be?

I dont want to change the fluid again and have it still toast, especially when there seems to be more problems than burnt fluid.

What is the current mileage?

90,xxxx
I ended up changing the fluid again, found quite a bit of metal shavings in the pan, so the trans has got to be toast.
Anybody have any luck with rebuilding them and getting some good mileage out of it?
Im thinking I need to get a used trans and throw it in, or rebuilding the current one, driving it until she gets it paid off in march then trying to trade it in on something else that isn't a piece of crap.