What you say makes sense, but the route and waypoints were pretty benign and were clearly displayed correctly when I select the imported trip and displays the list of waypoints and on the map. Regardless, the Garmin kept wanting me to take three earlier I-75 off ramps, but there was a reason we needed to pass by those ramps.
Calculation mode=Faster Time. Avoidances selected were u-turns, carpool lanes, unpaved roads, Toll Roads; there were none of these along the route. My old Garmin followed my route waypoint to waypoint to waypoint. And if I couldn't hit a waypoint for whatever reason, the Garmin would recalculate to get me back on my route.
FWIW, I've attached a copy of the route .gpx file.
Anyway, thanks for the feedback