Who played lead guitar on River in the Rain by Roger Miller?
If it's not Merle Haggard, or Merle Haggard's lead guitarist, it's someone who has embodied that style and reflects it perfectly.
For Roger Miller's Roger Miller album, that features the opening song River in the Rain, Discog credits:
Electric Guitar – Larry Byrom, Reggie Young
I would bet on Reggie Young since he's more reputed as a studio lead guitarist and has played with Merle Haggard for several albums, so your intuition was right.