cazabon, #Furnace update...
So, I wasn't going crazy. The replacement, stupidly expensive and complicated ECM motor they shipped me was in fact DOA. Confirmed with a 2nd replacement I got today. I was about half-convinced I had done something wrong with the first replacement, but couldn't even guess at what.
#Lesson: #believe in yourself.
I have now disassembled and reassembled this furnace more times in the past month than I've had #pizza in the same time, which seems #wrong.