Nah, I'm staying with OHP for now... I'd just like to see a bit more symmetry is all.Are you right handed? If so, you might just be unconsciously using your right side more than your left.
That said, if you're looking to work traps, hang cleans are better than overhead presses.
Deadlift - yes. Mixed grip - yes. I alternate grip every set (once or twice a week).Do you deadlift? If so, do you use a mixed grip often? IF SO, do you always use the same mixed grip without alternating?
Long shot, but I had trap imbalance from that a while back. I was doing the same with rack pulls and holding lockouts on both for a few seconds.