Are you still ziplock bagging or have you upgraded to a vacuum sealer, Mark?
I'd be concerned about the residual carbonation in the Dr Pepper blowing a ziplock bag open.
Maybe instead a reduction with the bag juices, Dr. Pepper and the BBQ sauce after it's all done and then mixing that in with the shredded pork. This is how I would do it if it were me cooking it. I'm not finding in-bag marinades to be all that great because of the amount of meat juice that gets trapped in there, further diluting them. I'm finding that dry rubs or fresh herbs to be more effective as they form their own stock as it cooks.
