Atlasman,
have you tried a different rest? Just curious. Something is not right, or you should get consistent groups. I shoot 5" vanes with good helical and don't have any problems with either 3 or 4 blade 100 Gr. muzzys. It doesn't take much to be out of tune for broadheads. I shoot strictly broadheads, and find that the best method for overall accuracy is to group tune to 50 yards. If you've got a tuning problem it will become evident as you get to around 40 yards. Best of luck in resolving your problem. I've been there and it really shakes your confidence when you get flyers from nowhere. One of my bows was just doing that. I sent it back to my pro shop to get ready for and upcoming hunt and was advised that my sight was loose. Could have sworn I checked it, but it appears that I hadn't. Sometimes its the small things that cause the problem.