Are both the left and right drive axle retaining nuts right hand thread? Can't get either side loose using breaker bar or impact wrench.

First of all, Yea they are right hand thread.

Secondly, this may sound silly but, make sure you remove the cotter pin and the retaining cap before you try to remove the nut.

Make sure you spray the heck out of it with a good rust penetrant like PB Blaster. I wound up using a socket with a 3/4 drive breaker bar and standing on it to break it loose, then I used the impact wrench.

Good luck!

Or you can try a low tech approach and use a striking wrench.
Cheers