Jim
I have loaned my copy of of "This Band of Heroes" out, so I am not able to do a lookup. However, the National Parks Civil War Soldiers and Sailors System lists a James D. Reed, as 1st Lieutenant, of Company "D" 25th Texas Calvary (dismounted).
His title as Captain may have come of the fact that as 1st Lieutenant that he may have been the ranking senior officer and therefore defacto acting Captain, of Company "D". I would think that this is the case.