Crill Miller was a 2nd Lt. in Company F, 6th Texas Cavalry Regiment until about the middle of May 1862. The unit had fought in the Indian Territiories, Elkhorn Tavern and Corinth I. In May the units reqorganized and some officers were not re-elected. They had the option to go back to the ranks or resign. When they resigned they were dropped from the rolls. Many went back to Texas and joined other units. Col. B.Warren Stone of the 6th was not relected and went back to Texas to recruit a new regiment. His replacement was Lawrence Sullivan "Sul" Ross who later became the brigade commander. Stone recruited the 2nd and a lot of the officers who had any salt went with him. You will find people from the 3rd, 6th, 9th, and maybe even the 27th. Go to the Texas Cavalry Brigade site and look at Company F and the 6th Texas Cavalry Regiment, and you can get more on your man. I will note that he went to the 2nd.
http://www.geocities.com/sixtxcavrgtcsa