Until recently Mapquest would work with Garmins, but not anymore. So I've had to get Basecamp and learn it.
Like others stated, not exactly intuitive. But Mapquest could be a PITA too sometimes. I dont have your model Garmin but I did get a route of my choice loaded and it worked using Basecamp. It just took awhile. Like anything new you have to figure out how it works and then adapt to it. Trying to make it work the way you think it should will just leave you frustrated.
I'm not defending the Garmins, there are things that could and should be better.
As someone else also mentioned, a backup plan be it an actual map or downloaded instruction via Google Maps is always a good idea.
2014 Coachman Clipper 17FQ
2011 Ford Ranger 4X4