Autoshifting out of the saddle
Yesterday I finally decided to change my chain after around 2k mi, stretch wise was decent but it was a little stiff. Cassette looked nothing like the picture of a worn cassette so I didn't change it.
So, after 2 rides with the new chain, I've noticed that when out of the saddle, or even on the saddle powering through a hill pulling hard on the handlebars the RD will auto shift 2-3 cogs to the left. First time it happened I almost fell. Would this have anything to do with my new chain? Should I change the cassette or just readjust the RD?