So, just as I got to the stage of assembling the Canon ipf8300 where you need 4 weightlifters to put it on the stand, UPS showed up with my Rear Carriage Bushing for the z3100. Props to LPS Computer for sending not one but two, just in case. Very nice.
So, I just got the Rear Carriage Bushing and put it on. That appears to have been the problem. Printer printed perfect Calibration and Profile pattern on HP Prem ID Satin.
So, any of you who want to convince your spouse that you "need" another wide format printer, just follow my steps here. Now I have a perfect printing z3100 and a brand new Canon ipf8300. Only paid $2500 for the Canon, after rebate.
I'll probably post this little tidbit in its own thread as well just for reference: If you need to replace or install the Rear Carriage Bushing on the z3100 / z3200, the manual tells you to essentially disassemble the ENTIRE printer just like you have to do to replace the belt. YOU DO NOT HAVE TO DO THIS (if you're careful.) Just remove the Right Cover. When you pull the Carriage all the way to the right, (use a bright light shining in there so you can see), you will see where the Bushing goes (look at the diagram in the Service Manual). I just used a pair of needle nose pliers to hold the bushing so I didn't lose it, and using a tiny 4 inch screwdriver (tiny like you could remove the back of a watch with it), was able to gently force the far end of the bushing into the hole. Then HOLD ON TO THE BUSHING WITH YOUR PLIERS, push or pull back that fleshy colored piece of rubber thingy in the way, and you can easily apply tension install the near end of the bushing into the corresponding hole. I just saved you about 8 hours of headache, and the likelihood that you lose/break your bushing again when you put the Carriage back on!