How long are your arrows? Spine issues will give you tuning fits but not at random like the OP states. You could just be torquing the bow. I'd number your arrows and see if a pattern emerges. Sometimes a simple twist of the nock will help you out. Now if your arrows are under 28" you may be on the stiff side. You state later on about a 125gr trick. Are you talking broadheads or field points? Since you call out 125gr I'll assume you are currently shooting 100gr heads? More information please. Also how many shots through the "new" bow?