“I did drag & drop both the route & track to the GPS in Basecamp; I even did some “adjustments” to the route from there. Once unconnected from Basecamp and installed on the bike, when I called up the route it was different from when it was connected to Basecamp!”
If you adjusted the route in Basecamp that won’t automatically change the route on your Nav 5. You have to re-import the changed route from Basecamp into your Nav 5 again as a different name, or remove the original route from the Nav 5 first then install your changed route.
Lots of reasons for your routing anomalies but the usual reasons are different avoidances set up in the Nav 5 than in Basecamp, or a different mapset in the Nav 5 than on Basecamp, etc
While this won’t correct a corrupt route it can help identify a corrupt route before you leave home.
After making the new route, then importing it into your Nav 5 bring the route up in the Nav 5 to verify that it is in the unit. Now upload the route from the Nav 5 back into Basecamp, change the color to something different than either the track or the original route then re-name that uploaded route to something that your recognize (like put a 2 after the name) now compare that route to both the original route and the original track. If it doesn’t match EXACTLY then something changed the route when it was originally imported into the GPS.
The above is a good way to catch a marginal or unstable route before you leave home and get part way through the trip.
I’m not sure how your Nav 5 fits into the Zumo series but Garmin posted this on their web site a while back about Basecamp and the Zumo series.
“The following devices are NOT compatible with routing in BaseCamp:
•zumo 400 series
•zumo 500 and 550
•zumo 660 and 665
These devices may appear to take a route without issue; however, when navigating the route, an error message may appear. An alternate program to use is MapSource(1). First download the map to your computer, then use MapSource to create and transfer routes to your zumo.
(1)Mapsource is only available for Windows computers.”