I also wonder if we are increasing the cognitive load by moving too quickly through the procedural. If the conceptual understanding leads to a certain level of procedural fluency can we stay there and play before we add all the things?

Going too fast is often the problem. Also, teaching two confusing things right on top of each other. How 'bout teaching adding positives and negatives, then doing a week of something else (starting each day w/10 review integer problems), and then going back to bring in subtracting integers?