It is a common problem. The routing algorithm in the GPSR is not the same as in the MapSource program; they sometimes choose different routes from the same map data. Two things you can do:
1. Set the routing options the same in both. I do not know the Vista C, but in my GPSMap 60C the options are in a setup page named Follow Road Options, where I choose fastest or shortest route, car or bicycle, avoid highways, etc.
2. Set enough intermediate waypoints (via points) to guide its little brain to the roads you want. It looks like you have already done that.
Having learned its idiosyncrasies, I can get my 60C to route where I want. If these tips do not do it for the Vista, you are welcome to send me a sample route in a MapSource file by email (see my profile) and we can discuss it in more detail.