I would say it skips a stitch about every 2-3 inches. Sometimes a lot less, rarely more.
When switching from a 50wt 2ply, to a 50wt 3 ply, I wouldn't think a tension adjustment would be needed. I never have to adjust the tension on any of my numerous other machines switching even from a 50wt to a 60wt. From 50wt to 12wt, sure.