" Didn't watch (at Costco). Snapped a wheel stud. When I asked what and how - he had torqued them, he indicated he used his *air impact* and had set it for the specified torque. "
That is NOT the norm for Costco.  I have bought MANY sets of tires from them over the years.  They have always lightly ran the lugs up snug then hand torqued.
Now good OL LesSchwab uses a torque wrench for show AFTER they have blasted the lugs up.  Funny how they click as soon as the wrench is turned!
Discount Tire has been good at proper torque also.