Jack, the 3 is not flatted in a major pentatonic.
to the best of my knowledge, regardless of the number of notes in the scale, if you flat the 3rd it is minor.
@davidsoleil , you might look at some tunes. like Sally Good’n, or Katy Hill, You would have to remove minimal notes to play these pentatonically.
The problem you will run into in bluegrass is that most songs aren’t strictly major notes…bluegrass has a large blues influence which incorporates liberal use of the flatted 3rd and flatted 7th quite often…playing using only major notes creates an “overly happy” mood .and diminishes much of the “feeling” of the style.