Shirley,

I found this on the Soldiers and Sailors System.

H.C. Gray private, Company G, 2nd Texas Infantry

H.C. Gray .... Company D 2nd Regiment Texas Infantry
( State Troops 1863 - 64 )

The 2nd Texas was from the Houston - Galveston area.
If your Grandfather was from that area at that time then this may be him. I think both records may be him because many men of the 2nd came home after Vicksburg in 1863 and stayed in Texas, so he could have been in both units.

I hope this helps,
Gary D. Bray