You tell me: "From this, I believe McMahan assumed command of Company G in August, and returned to Company F on the resignation of John Muller, October 4, 1862." You may be right. Chance (referenced above) states that John Mueler was killed near the breastworks of Robinett on 4 Oct. The term "resigned" is a bit bizarre in this context. Hood is listed as being wounded at Shiloh.

Thank you very much for the sources.