This helps explain the disparity. Your situation for Tulane is a GREAT one, OP! As a PT award winner, you may want to ask Tulane if you were to live on campus whether they would award you some need-based aid. Living on campus (and off campus but nearby) might give you a very different ‘New Orleans’ experience than the one you’ve had all your life.
the PT award is covering tuition/etc, but Tulane might make it possible to live on campus too, just something to try since your package as it is probably doesn’t include need-based aid. http://www2.tulane.edu/financialaid/grants/nola.cfm
You should at least contact them to ask, especially with TOPS, PT award, Pell and low-income all in the mix. BTW - congrats on PT award, that’s a fine accomplishment! My guess is they will fight to keep you. You probably don’t even need to mention the amount of the USC and Emory awards. Just say you are struggling making a decision, and let them see what they can come up with.