Ok so I did some more testing today with surprising results.
First of all the car adapter I purchased was this
Amazon.com: Scosche reVIVE II - Dual USB Car Charger for Samsung Galaxy Tablet (GUSBC3): Electronics
I made the same 30 minute drive today. I had wifi, bluetooth, gps, sync, and screen rotation on. I made sure the only thing I was running was navigation. I went the same route to and from my friends house. Regardless of if I was in the 2.1a slot or the 1a slot I had just about the same increase in battery, 10-11%. I saw no increase with whatever slot I put it in which leads me to believe that the phone has an internal limitation of a 1a charge. I will have to do more testing because the fact that the stock wall charger was 2a was very odd. There could be reasons for this but I am not sure why unless they do this to make the charger more compatible with the larger tablets. I did notice the other day that the wall charger did not charge as fast (actually pretty slow) if I had a lot of apps running in the background which makes sense because as you use more resources the battery depletes faster. This all leads me to believe that the internal restriction of the phone is 1a.
Has anyone else found any similar results?