First, please reference the information Garmin provides in relation to the ES upgrade:

http://www.garmin.com/us/intheair/ads-b/seven-questions/

There is perhaps a misconception that simply having your Garmin GTX-330 transponder upgraded to include Extended Squitter capability is the only step for ADS-B Out compliance. As with almost all ADS-B installations, appropriate interfacing to other systems in the aircraft (ex. approved position source & altitude source) is required along with approved guidance material that indicates the airworthiness approval procedure followed for return to service of the aircraft (ex. AML STC). Garmin provides an Installation Manual with Approved Model List STC for its Aviation dealers. Authorized dealers should not be distributing the necessary data and paperwork for the ADS-B installation to non-dealers.

As with all ADS-B installations, Southeast Aerospace strongly recommends that you only contact and consult a trained, authorized avionics dealer.