A impact helps but its not a must-have to get it off... ... but you do need a decent breaker bar. Not sure what a torque wrench is supposed to be able to do. 5' is not enough leverage. What brand breaker bars are you breaking?

I doubt any shop would break loose an axel nut and let you drive home with it loose for liability reasons but who knows..

My two cents... get a decent 3/4" or 1/2" breaker car/socket and if you have a a nice long pipe to slip over it (I'm using a 6-8 foot DOM tubing) that is the way to go unless you have access to a really nice, heavy duty impact gun (my 700 ft-lb ingersoll rand also didn't have any issues zipping off the axle nut)