#1- Only train 3x/wk and focus on squats, deadlifts, bent over rows, military presses, and bench work.
#2- drop the arms to eo wk, and only do 6-8 sets/ bi's as well as 6-8 sets for tri's
#3- lower the weight and focus on more repetitions(20-25/set). People say that you have to go heavy and low reps but I believe if you have stubborn arms then focus more on getting a good pump and mind/muscle connection, the arm workout's purpose is just to stimulate the fibers, the infrequent training of them and more compound moves will help them catch up. Also, because your only training 3x/wk and only doing arms eo wk, overtraining wont be a problem.
This is something I've been doing the past month and it seems to be working pretty well, my arms are 18 1/4" cold, 18 1/2-3/4" pumped, and I'm currently off juice. I'm really hoping to break the 19" cold mark by next spring. Just something different I've been trying instead of the whole priority balls to the wall perspective. For stubborn arms, back off em'