Not sure I’d get too caught up on the the small transfer slot exposure.
Mine idles at 950 in park with very little t-slot exposed. I would suspect air is coming from somewhere else, or as RRR mentioned timing.
Hey Mark. Yeah, mine idles about 1000 in park and 850 or so in gear. It all works well that way, I was just surprised to see no exposed transfer slots with that kind of idle speed