As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
N1 VIBRATION REACHED 2.6 IN FLIGHT AIR RETURN TO DEN VIBRATION 2.6. SWAPPED N1 FAN PICKUP FROM LT TO RT IAW AMM 77-11-01. PERFORMED PWR RUN WITH CREW. VIBRATION INDICATION APPEARS TO BE ERRONEOUS. ACFT SAFE FOR ONE TIME FERRY FLIGHT FROM DEN TO STL.