Mark, is there any pattern that you can see when this occurs? Does it begin after a random number of shots fired, or after a right then left (or vice versa)? Try to determine that to help figure if it's recoil related, or otherwise.
If all else fails, and it were mine, I'd send it to Phillip Crenwelge in Emory, TX. He is a gunsmith of German descent and is the finest trigger man I've ever known. He has sorted out many, many issues with triggers on all types of guns. It may even be worth a call to him just to talk about it. He doesn't always answer during his working hours but he'll usually return the call. His number is 210-313-5988.
