If you are traveling as a revenue passengers, your D3 status technically won't help you. You will be handled as revenue, prioritized based on your AAdvantage status. If you have no AAdvantage status, you probably won't get an upgrade. Upgrades like that only come in an oversold situation - resulting in EXPs, Plats and Golds getting the business class seats first. Most of the time D3s are accommodated after revenue passengers.