You mention that you like the bibs without the infused grippers, but then you say you purchased a couple of pairs with the gripper of the same size and brand (assuming these are two different models?). So are we talking 3 different bibs here? And one set of bibs with grippers causes irritation, but not the other bibs with grippers? I'm a little fuzzy on what factors we're dealing with here.

I will mentioned that leg hair could be a factor. Grippers can pull on leg hair and make things pretty uncomfortable. I've also noticed that grippers work better with shaved legs. I had some insulated bib knickers that would NOT stay below the knee if I had hairy legs.

EDIT: I'll also add that manufacturers have different "cuts" or fit profiles within their brand. If you bought the same brand, but one set of bibs had a "fitted" profile and the other had a "semi-fitted" profile, the fitted profile will definitely be tighter around the thighs.