LOL. So true.
Seriously, Damner, if you work on getting your numbers up in pulling exercises like Deads, rack deads, face pulls, etc... your traps are going to grow. Now, the really heavy back exercises are also going to tax your grip to a great amount (don't use straps if you really want to develop your forearms). And guess where the muscles are that are responsible for grip? You guessed it, in the forearms.
So, as PozzSka so simply put it in the above quoted post, if you add some serious weight to your deadlifts, and other pulling exercises your traps and forearms are going to grow.
Also, if you really want to bring up "lagging" body parts, then simply choose variations of the basic exercises (the ones that will allow you to increase the most in terms of strength) that put secondary emphasis on these muscle groups and throw a couple isolations in if you still feel the need.
In regards to the 5 day split, yes, it does allow one to focus on each body part better. But, focusing on each body part isn't necessarily a good idea for a beginner like yourself. That is something that a very advanced trainee might do (like a professional bodybuilder) to really make sure that they build maximal symmetry and proportion. It is not all that great of a plan for someone looking to put on an appreciable amount of mass though.
You would probably be much better off doing either an Upper/Lower split, a Push/Pull/Legs split, or even a Total body program. All of those options are going to be much more conducive to gaining large amounts of muscle. Like I stated above, if you honestly feel like certain muscle groups are lagging, then choose variations of the money exercises that put secondary emphasis (or even primary emphasis) on those body parts.
For instance, lets look at triceps since we already addressed traps and forearms to a degree. All pressing movements are going to put either secondary (as in the case of bench, military, etc...) or primary (as in the case of vertical torso dips, close grip bench, etc...) emphasis on the triceps. So, in short include a lot of pressing movements, and work on getting a lot stronger in those movements and once again, viola! Your triceps are going to grow. If you really feel the need, it's okay to throw in some other isolation exercises (once again try to pick ones that will allow you to make big jumps in weight, kickbacks aren't a great option, while skullcrushers are).
Hope this helps.