I would lay money on this being, primarily, a trigger-control issue.
Do dry-fire drills (triple check to make sure pistol is empty) until you can press the trigger without the sights moving.
Do "Ball and dummy" drills (live and dummy rounds mixed at random in magazine) to make sure you're not flinching and/or anticipating recoil.
Links to a few articles worth checking out:
cross-dominance:
http://pistol-training.com/archives/433
ball & dummy drill:
http://pistol-training.com/archives/210
"correction target":
http://pistol-training.com/archives/292
tons of good stuff on that site.