i like how you're doing push pull......my workout is similar to what you do....and to be honest- probably just because of my genetics- but my arms grow faster than anything... My chest is what lags....
monday- Chest, Triceps, Shoulders
Tuesday- off day (but u could throw in ur abs)
Wednesday- Back, Biceps, Forearms, Traps
Thursday- Off
Friday- Legs & abs
people normally question me on my wednesday "doesn't that seem alittle much for one day?"....i can get my workout done in under an hour and 10 mins w/no bull shit...i'll do three exercises for my back (rows, lat pulls, w/e else) and i'll do 3 sets of each trying to get 10 reps (but in reality i'll only get 4, 5, or 6 on that last set.....same goes for my biceps, forearms i generally will just do some forearms curls w/dumbbells, and then traps just 4 sets of shrugs....Remember that you have 5 muscles in ur arm (simplified - not including brachialis, delt, etc.) but u have Biceps (2 headed), and triceps (3 headed)...so reasoning would tell you to work ur tri's hard, since they make up the majority of your arm