I'd be inclined to change my flight arrangements even though that might be a problem given how busy those routes are! Even without anything significant to carry, it can be a chore. Plus you don't even have your boarding pass for the AA flight since you are not checking through on the same airline or alliance. Plus since the flights are so busy, they may not leave on time as they are sorting out the standby list etc etc., although with the Sh*ttle I notice that they sometimes close the doors and leave sort of on time even when there are a few empty seats and hundreds of delayed, angry passengers waiting to board.

Even within the same terminal I always leave 45 minutes to account for the usual 5-15 minute late arrival, deplaning time etc etc.

I guess you can always hope that AA is late departing. At least AA has a later flight.

Good luck.