Nice! I've been following the thread since I last posted, impressed at the depth of the troubleshooting skills going on here.
I feel confident it was the Duralast unit in my case also. When it occurred, I even went back and swapped the three different units back in, just to confirm that these codes were being thrown consistently at each change. Yep, Duralast...327 code. Anything other than Duralast...no 327 code. Bizarre.
Anyway...glad you have solved it. Enjoy your well-earned Scotch!