Have you tried slowing down the chord changes to a snails pace? I do this when I start getting frustrated about a technique that is hard for me to perform. Take a break from the guitar, then when ready to come back go at an extremely slow pace....like.....really.....really....slow!

After you have done this a few times and you feel ok with the changes, you can start to speed it up a little incremently.

Also, I sense you are trying to be something of a perfectionist? Don't get hung up on occassional off-notes or buzz strings. Move on to something else to take your mind of your frustrations. You can come back to where you left off another time and you will probably find your technique has improved.