Either reading comprehension is lax or my original post is unintelligible. I did mention that I isolated the cables, housings, and caliper. Here's what I found:
1) Cable is flawless. Regardless, I cleaned it with Simple Green, and re-lubed the entire length of cable.
2) Cable moves completely without friction in the front housing (the housing that runs underneath my bartape). This is 1 year old housing.
3) There is absolutely no friction in the brake lever. The thing moves freely.
4) There is a small amount of friction through the rear housing just before it enters the caliper. Though I would expect the spring tension to easily overcome this small amount of friction.
5) Upon removing the caliper from the bike (and detaching the cable), when squeezing the calipers with my hand, I felt very little friction. However, when releasing the calipers slowly, I could feel stickiness in its movement.
6) After I reassembled everything, I still have the problem of the brake not fully releasing.
I feel as though this "stickiness" upon release, combined with marginal amount of friction in the rear housing is keeping my rear brake from fully releasing when I release the brake lever.
I've since found a nice Shimano brake diagram and Park Tools writeup (which is pretty poorly written IMO). I will attempt to disassemble the caliper and clean/grease the pivots. Hopefully this will resolve my issue. I'll probably replace the rear brake housing since that is 4 years old now (or simply drip some lube through it).
Thanks to everyone who posted helpful comments!