Medical and Surgical History of the Civil War (Yeah I'm shortcutting the name) Volume 11 page 222
461 Preston, Y.P. Pt. C. May 15 died June 8, 1864
42d Alabama 15, '64
This is how it is written in a table. I don't see a Y.P. Preston on the Soldiers and Sailors site Yet this guy with the same dates as Thomas P Preston in your post is listed as a private. I'll leave it to you experts to figure out.
The table he is listed in is "Condensed Summary of Five Hundred and Thirty-three Cases of Primary Amputations in the Upper Third of the Femur for Shot Fractures [ Recovery 1-260 Death 261-528 Result Unknown 529-533] (note that the numbers refer to the numbers for the individual men listed in the table. This Preston is number 461 showing he is in the numbers under "Death") The intro for the volumn says "It was impossible with the clerical force available to make more than a superficial examination of the individual cases of the immense series of nearly sixty-thousand flesh wounds of the lower extremities..... (there is a bit about how they tried to make the numbers a bit more manageable)....Of the series of Flesh wounds of the lower extremities, six hundred and seventy-four were punctured or incised, and fifty-eight thousand seven hundred and two were shot wounds....."
There wasn't any further info on this Preston.