You must have overlooked a number of documents. The soldier's service file includes a record from Chimborazo Hospital No. 2, Richmond VA. This shows that he was admitted Dec. 18, 1862, and sent home on furlough for 35 days, Aug. 15, 1863. Other hospital records show date of admission as Feb. 18, 1863. At any rate he cold not have been with his regiment during the Gettysburg Campaign or afterwards.

Later records show him to have detailed to the Quartermaster Dept. Mar. 7, 1864, assigned to Capt. J. A. Kerby, Cassville GA. Capt. Kerby's men retreated to Atlanta in May 1864. Shephard's company roll shows him absent on detail, August 1864. No record afterward.

The soldier probably participated in noteworthy battles which took place during 1862. Perhaps you should focus on the Seven Days, 2nd Manassas and Sharpsburg.
http://www.nkclifton.com/amer-civ-war/Georgia/11th-Georgia-Infantry/11th_Georgia_Infantry_Regiment_CSA.html