Agreed, take a shot at the cheapest solution first if there are no codes thrown. If there are codes, it could be something you can deal with, or a cheap fix at the local shop. If there are no codes, try the fluid flush. I wouldn't waste the money on Mobil 1, since you don't know if it will actually fix the problem or not, so why waste more money than you have to. If the flush works then you can always go back in a year or so and flush and fill again with Mobil 1.

If the tranny is bad be prepared. Out of curiosity I priced out replacement trannys in my area, just in case I ever needed to get one. Best price I could find was $1800 for a rebuilt unit with a 12 month/12K mile warranty. That did not include labor for installation, that was just the price for the trans. Add another $700-$800 for the installation. This kills me though, you have to pay a fortune for a poorly designed, poor performing (even when new) transmission.