With an impact wrench the stud will stil turn but usually the nut will break and rotate about 1/8 turn before the stud catches up. Therefor take the imact wrench and socket. Best to use no extensions, with the impact in place, hit an release the trigger severeal times just enough to allow the socket to start rotating and then come to a stop. Just keep at it untile the nut comes off. If this fails try a bigger or newer impact wrench.

Of coarse penetrating oil helps.

John Roncallo