Follow up on the above:
Have done some experimenting with your suggestions and what seems to have helped this issue is:
1) Adding more rub mid cook. If I put the meat on at night, I will add a new layer of rub upon waking up in the morning. I apply it to the meat right on the rack of the smoker.
2)Increasing the smoker temps during the second half of the cook, to help the meat get done faster. From your comments, I assume this keeps the spices from diluting as much since cooking time is now shorter.
My most recent packer brisket had a great bark, both in texture and flavor. The bonus was that it cooked in about 3 hours less time than usual, due to me increasing the temp during the 2nd half of the cook.
Thanks to everyone for suggestions.