3.4 rc6 much better alt hold?

Were there things done to the code to try and improve alt hold since 3.4 rc1? I just flew rc6 and it seems greatly improved.

It’s very possible. A lot changed from -rc1 to -rc6. In particular the jumps between -rc1 and -rc3 were quite huge. There were a fair number of EKF changes in particular during that time. Not so many changes to the control algorithms, so it’s most likely that the improvements come from Paul’s work on the EKF.
Thanks for testing and providing feedback!