I am trying to lower my body fat percent. I am currently at 19% and have stalled out twice at 15%. I am trying preserve and maybe slightly increase muscle mass. I gain muscle and fat easily but tend to lose both when I try to cut down.

Oh, here's one trick that may work, my trainer taught me.  See if this works...like I said, I'm not an expert.

I used muscle confusion.  I change my work out and intensities every 4-6 weeks.  I go up on intensity, and change my workout (type of exercises).  I have never hit a plateau since.  I think Power90X does this, but my CPT says it a good way to restart the body after a plateau.

Also, I never eat the same amount of calories a day, some days 1600, some 1800, some 2000.

I have also heard that is correct about protein, which is why I cringe when I see protein shakes advertised as having 50g in them.  How is that helpful?  

Okay, good, you are not hard lined on anything, which makes tweaking to you must easier.  

I would suggest you make sure you get in your fish oil regularly and this is regardless of which plan you choose.  You can get Omega 6 from even beef, but Omega 3 in the form that we need it pretty much only comes from fish oil.  I say pretty much because it also comes in seaweed, but I refuse to accept that.  That's just my own taste bias.

I would absolutely agree with muscle confusion, which is why most on BFL change up their exercises every 3-4 weeks.  I prefer 3 for me personally, but that could be because I'm ADHD and get bored easily.  

I am on a 4 week cycle of exercised and correlate it with taking pictures during a challenge.

Here is a chart of my body fat percentage every Thursday morning over the past 22 months

Your charts make my OCD so happy.  

How are you measuring your body fat?

Here is a weekly Total body weight chart comparing 2009, 2010, and 2011

Omron HBF-306C Fat Loss Monitor, Black

www.amazon.com/.../B000FYZMYK

you can proccess more than 30g lol cmon guys

That was a very specific answer.  :)

Mike Harris swore those things were no more accurate than a magic 8 ball.  I'm assuming he was somewhat off on that, but the point is that I bet you're making more progress than you think.  

Regarding protein absorption

www.wannabebig.com/.../is-there-a-limit-to-how-much-protein-the-body-can-use-in-a-single-meal

I'm always suspect when a scientific article endorses a supplement.  In this case, Alan has a deal with them.  I'm not saying the supporting evidence is bunk, but now we have to be more suspect.  

nerdfitness.com/.../60-pounds-overweight-to-6-pack-abs

Alan Aragon sounds fake and very Lord of the Rings. Plus he was using justifying logic and not science.

It's funny how logical isn't always truthful. 

It does seem, however, that Tom Venuto agrees.  Tom takes a different approach, one I personally find more compelling. 

http://www.tomvenuto.com/asktom/protein_grams_per_meal.shtml

We sometimes believe things to be true that we've heard over and over again.  Booster shots / inoculations never cause autism.  They never have.  It's scary to think how many people thought so.  Sorry Jenny McCarthy, it's been proven that you're wrong.