TB Shearman was the son of John H Shearman a strong but elderly supporter of the confederate cause. Locating from Virginia in 1832 he was a farmer and wagon maker of some repute in Monroe City, Marion County MO.

TB Shearman died in Fresno California which fits Mudd and UCV list.

TB stands for Thomas Benton. He has a draft registration:

Name Thos B Sherman
Marital Status Unmarried (Single)
Race White
Age 24
Birth Year abt 1839
Birth Place Missouri
Residence Date 1 Jul 1863
Residence Place Jackson, Monroe, Missouri, USA
Congressional District 9th
Series Number Nm-65, Entry 172

He was clearly arrested and held under purview of Macon City authorities as a citizen, but as this letter states he was with the rebel Porter.
https://www.fold3.com/image/257188075/shearman-thomas-b-page-1-us-civil-war-service-records-cmsr-confederate-miscellaneous-1861-1865