You might post a query on the Civil War forum, see if anyone knows where those two Regiments originated.It might help to decide which is your Wilson Davis.
1880 census Miegs Co, TN, looks like Ples still in TN:
NameRelation Marital Status Gender Race Age Birthplace Occupation Father's Birthplace Mother's Birthplace Pleasant DAVISSelfMMaleW56TNFarmerTNTN Sarah DAVISWifeMFemaleW52NCKeeping HouseNCNC Amand J. DAVISDauSFemaleW18TNTNNC John N. DAVISSonSMaleW15TNWorking On FarmTNNC Lawrence J. DAVISSonSMaleW14TNWorking On FarmTNNC Mary M. DAVISDauSFemaleW12TNTNNC Charles F. DAVISSonSMaleW10TNWorking On FarmTNNC Martha DAVISDauSFemaleW8TNTNNC Peter W. FORKNERCousinSMaleW23TNLaborerTNTN Cuff ELDRIDGEOtherSMaleB22TNLaborerTNTN
There is a Wilson Davis, divorced, up in Hawkins Co, TN 1880 census:
James ALLENSelfMMaleW30TNFarmerTNTN Mary E. ALLENWifeMFemaleW29TNKeeping HouseTNTN Paralee ALLENDauSFemaleW2TNAt HomeTNTN William ALLENBrotherSMaleW22TNFarm LaborerTNTN Wilson DAVISOtherDMaleW60TNFarm LaborerTNTN
Since Wilson and Ples were in Monroe Co, TN in 1860, I think I'd look for divorce record in that county, see if it fits Wilson and Elizabeth data.
Have you checked the cemeteries on the Grayson Co, TX GenWeb on the archived site?http://www.rootsweb.com/~usgenweb/tx/grayson/graystoc2.htmhttp://www.rootsweb.com/~usgenweb/tx/grayson/graystoc2.htm There are 117 entries for Davis, so I didn't go through them, but you might want to.Maybe one of his children or his brother erected a headstone for Wilson.