There were... problems that are thankfully now resolved. Turns out I tightened the roller screw too enthusiastically (ask the castle nut on my AR-15 about that. 💪)
The roller screw of the new extruder was too tight, which impeded filament travel. This in turn caused the filament to reach the nozzle too slowly, creating a heat-to-extrusion delay. This caused the filament to start melting before it hit the nozzle, and it built up to the point that the entire feeding process locked up. I could only get about 20 minutes into a print before everything ground to a halt.
The extruder kept trying to compensate by backing up, backing up... and it progressed until nothing could pass. The entire tube became filled with semi-melted plastic. I had to disassemble the entire hot-end assembly, heat it to 260C, and work the clog through until everything cleared. What a pain.
After loosening that screw a turn, everything was back to normal.
Now I can resume printing nuclear weapons!