Hi Robert,
This sounds like the typical case where the new screen has to be programmed with the MtSN from the old screen. I realize you did the Display IC swap, but I'm curious as to whether that's where the MtSN is stored or if there's somewhere else on the display that holds it.
Couldn't hurt to give it a try; I have no idea whether you can still read it off the original screen without the Display IC, but of course you can always pull it directly from the phone with either JCIDRepair or 3uTools.