For completeness' sake, I'm posting the follow up.
I got a nice brisky from my local butcher and used Kosmo's to inject once again. I added some rub and water to the mix and injected as I had done previously (where i FAILED). It was very good. Clearly my problem had been the enhanced cut of the WallyWorld meat. I took 10th out of 44 in brisket that day. Plenty of room to improve, but I was pretty happy that the hamminess was gone. Check your labels!!!
Pork Butt and Chicken Legs (semi-retired)