I truthfully don't think you have a problem with proud cut or cryptochridism. Nothing you've said rises to the level of studlike behavior.
I think you have a problem with turn out. Some people turn our mares and geldings together with no problem; some people/horses, it just can't be done.
Your gelding is acting the way he does because being turned out with the mares has activated some protective/stud like instincts in him. I have a gelding who acted somewhat the same way when turned out with a mare, now that I'm back to three geldings, everything is back to normal.
Try turning him out by himself for a couple of weeks before ordering bloodwork.