I think the stock plug is tourqed with an impact gun at the factory,judging by how many I've had strip out when I go to remove them...I found using just the ratchet with NO extention gives you a better chance of loosening it ,it seems extentions dont fit as tight or are made from softer steel and will round out the square recess in the plug...I've had to heat the diff housing with a torch or weld a bolt into the stock plugs many times..I drilled one out once and used an E-Z out,one of the few times I've NOT busted one off in what I was trying to unscrew!..had to pull the diff cover and wash out all the chips from drilling too..I like using brass pipe plugs with a hex head,or a steel one ...
GM and other makes used those stupid recessed plugs on engine blocks & heads too,and are often impossible to remove ..had many a bad day at the auto parts stores machine shop because of those dam things!...