Did you replace the axle, did you get a new nut, what did you do to the car. If you reused any of the parts I'm sure the threads are slightly gauled (my spelling sucks, but read messed up). Also the axle nut is designed to dig into the threads of the axle to act as a lock to keep it from backing out in addition to the "tab". I don't mess with torque wrenches when putting the nut back on, I just use the impact to seat it, and then another good 5-7 blows to 'torque' it down.