I just looked up the Garmin 770, it looks perfect. I have an old Garmin Nuvi 2797 which has been discontinued. It is great and I'm sure the 770 has the same features. You can read the screen in bright sunlight, very important. It is not poloroid in the wrong direction. I had one that when I put on my polaroid sunglasses the screen went black for me.
It has lifetime maps,& traffic. And the biggest feature for me is I can upload GPX map files, so it goes where I want it to.
Never follow a GPS unless you look at the whole route, this is hard to do with the GPS unit.
Garmin gives you a free map program for your computer that you can download to your computer called Base Camp. If you plug the Garmin in and do a map update, you can select update maps for Base Camp at the same time. The maps on Garmin & computer are the same.
Now program your trip on your computer, make sure it goes where you want and save it. Then just click upload to Garmin and the track will be the same. Basecamp is not the easiest to use and it takes some learning and practise, but after that I program all my trips this way. If you still have MS Streets 2013, you can program and save a GPX file and copy it to the Garmin.