Is it possible your 29 T gear is worn? Did you put a new chain on?
Of all the things I tried, the most important was cable tension (doh!) and getting the jockey wheels properly oriented (doh!).
Maybe your RD limit screw is pushed in too far (or pulled out too far) and your chain doesn't line up exactly with the center of the 29T cog?
You may like to experiment on the stand (carefully) with limit screw position +/- 1/4 turn increments until it gets better or worse, you get the drill.