With your biglaw aspirations, I don't think this is a tough decision. Just transfer. In fact, you should be able to get into a T10, but if GULC is all you've got then you should go there. AU doesn't have the best biglaw placement and in this economy you need every edge you can get.
Also, you shouldn't worry too much about grades. You'll probably do well at GULC. I made a huge transfer jump (T4 > T20) and my class rank actually went up. This is, of course, only an anecdotal account, but it's pretty common for transfers to be successful at their new schools.