Even if you could get a list of ingredients, and even if it was complete enough for you to make your decision on that basis, the menu could change by your flight date. Getting a list of ingredients for whatever they'll serve on some future date isn't practical - nobody probably knows unless the flight is less than a week out. If they can't promise a gluten-free meal, bring your own food. (A world traveler cousin of mine has the same requirement. That's what she does.)
Another reason is that special meals can miss flights just like people, flights are moved around, and people change flights for any number of reasons. Special meals don't always follow. If you have your own food and your AA flight goes mechanical, you can take the UA reboooking they offer and not worry about the food part.
... Even ifyou switch to ex-JFK transcon flights I would be suspect of airline catering if I had a food allergy.
Given your need for gluten free food, and your past experiences, I would not trust AA or an other airline to correctly cater the proper food even if you ordered it in advance.
I'm not that pessimistic. Special meals for medical (or religious) needs are generally not prepared in the same kitchens as standard ones. The folks who prepare them know they're dealing with medical requirements, in some cases with potentially serious consequences. This is drilled into them over and over. Nothing is ever perfect, but of all the things to worry about, having a meal mislabeled in this regard is way down the list.