Virginia Historical Society. Manuscripts Mss3 L515 a - Robert E. Lee Headquarters Papers, Box 2, Series 5, Reports, 1863–1865, of Cadmus Marcellus Wilcox, Folder 7, Reports, 1863–1865, Item 26, Reports, 1863–1865, by Cadmus Marcellus Wilcox concerning operations at Salem Church, Battle of Gettysburg, Battle of the Wilderness, Battle of Spotsylvania Court House, Cold Harbor, Petersburg, Ream's Station, Bellefield, Evacuation of Petersburg, as well as the retreat and surrender [bound volume]. Typescript transcription is available.

Wilcox's reports should address your question. Some were published in "OR Supplement," but I'm not sure about the one covering July and August 1864.