Drug cartels have been using old airliners to smuggle cocaine for years. A Boeing 727 or something similar could achieve the flight profile described in this incident.
https://www.theguardian.com/world/2010/nov/15/south-american...
https://www.theguardian.com/world/2010/nov/15/south-american...
Although Southwest flies 737s and the SWA pilot did report it was bigger...
Could be a routine ferry of Nightwatch/NEACP based on the same profile, but seems like NORAD and WADS would have caught that sooner. And kiboshed FOIA and not made public statements and all that. Nightwatch is operated by USAF, though, under high classification, while WADS reports up through the National Guard. Miscommunication seems at least plausible.