Progressive Overload Strategies for Specific Body Parts

Mark,

I'm 1 year into training (if you count 6 months of P90x). I'm finding that using increased load for progressive overload is easier for some body parts than others. I do a body part split routine currently and I can do this load strategy well for back, chest and legs, but I have difficulty increasing loads of 5 lbs on smaller parts like arms and shoulders. Is this a common problem? Should I incorporate other forms of progressive overload? Do certain body parts respond better to those forms than others?