Dockman, in case your wondering about the above comments, and since you siggy says still trying, I am gonna step across the line a let you know...
1. There are many of us who are concerned that people learning how to do brisket cooks successfully add to much to the process too soon, complicating the process and making success much harder to gain.
2. You are adding a lot of sugar to the surface of the meat with a soda pop marinade, this is going to cause over-darkening, if not downright burning of the meat. Often with a brisket, you will end up with a very hard bark as a result of too much sugar added.
3. Beyond just the time, cooking below 225F often leads to drying of the surface of the meat and to a hard and dry surface to the meat. Even though you can still end up with meat that is tender, it is often dry to the mouth. Some of us feel that going hotter aids in learning a successful cook.
4. Now why then, do we hear of other cooks saying such low temps and long cooks, there are two reasons, one if that they are cooking a lot of meat in big cookers, that just have a different way of cooking. Others are using a type of cooker, be it a water smoker or gas cooker, that has a moist air characteristic.
Still, it's your meat and I wish you luck with your cook. Your plan could work just fine. Be patient and make sure you get it cooked until tender to a probe.
I'm feeling bearish, and I'm packing a Wusthof Grand Brisket slicer from MABA
"perhaps...but then again...maybe not..."