Here's some information you can cut your teeth on. There's need for more investigation on his capture on the retreat from Big Black, he may be been detached from the regiment at the time. It getting late and I'm heading for the barn out here on the Left Coast.

27th Regiment, Texas Cavalry (Whitfield's Legion) (1st Texas Legion)

27th Cavalry Regiment [also called 1st Texas Legion] was organized during the spring of 1862 using Whitfield's 4th Texas Cavalry Battalion as its nucleus. Many of the men were recruited at Daingerfield, Clarksville, and Paris, and in Titus County. After fighting at Elkhorn Tavern as a battalion, only 9 officers and 111 men were present. The unit moved east of the Mississippi River and was dismounted. It then fought at Iuka and Corinth and during the fall was remounted. Later it saw action in Mississippi, was assigned to Ross' Brigade, took part in the Atlanta and Tennessee Campaigns, then returned to Mississippi. This regiment was organized with 1,007 officers and men, lost twenty-two percent of the 460 engaged at Iuka, and surrendered only a handful on May 4, 1865. The field officers were Colonels John W. Whitfield and Edwin R. Hawkins, Lieutenant Colonel John H. Broocks, and Majors Cyrus K. Holman and John T. Whitfield.
http://history-sites.com/

See: http://gen.1starnet.com/civilwar/27cvmain.htm

http://www.rosstexascavalrybrigade.com/27thtexascavalryregiment/index27.html

http://www.google.com/search?client=safari&rls=en&q=27th+Texas+Cavalry&ie=UTF-8&oe=UTF-8

Company A Muster Rolls [partial]:

May & June,1863 Recorded as Present [Big Black was May 17 & he was recorded present?]
July & August, 1863 Captured in retreat from Big Black
May & June, 1864, Absent in arrest prison