I would return the axles you bought and rebuild the Stock ones (if they were, in fact the stock ones) OEM are better built and as long as you dont mess up the balance during the rebuild, you shouldn't have this shudder issue.
Plus rebuilding them with Rockford thermoplastic CV Boots, is a much stronger option over the cheap rubber that you'll get from alot of aftermarket companies, its a thicker and stronger material.
I was hesitant at first to rebuild my CV's but its really easy. Just a greasy mess. So be ready.
I can provide the Rockford link along with a build thread from the man who discovered Rockford's work on our pathy's if you would like?
Plus, having a chilton manual as helps alot as well, because it has torque values on top of the fairly clear instructions, if you have some mechanical inclination. the book is your friend.
-Kyle