First - we have been Xrayed every time we have crossed at Columbia for quite a few years now. The first time they told wife and dog get out and wait a few minutes - no water - no food - no book to read - 2 hours later I finally got through the Xray. They never go in to look around - they just Xray. The last time through coming into Mexico we got Xrayed in this direction too - we have been told the US bought Mexico the machines so they are using them. Expect this to eventually happen all the time at every crossing if you are in an RV. If you Congressman or Senator voted for the Patriot Act or supports that particular legislation that suspends your rights under the Constitution you are not going to get very far with them - or get any sympathy from them. They have spent billions "securing our borders" and will probably go to spending trillions and still there will never ever be a way to completely secure the borders. You can expect the border crossing to take longer and longer as they continue to attempt to secure. Anyone with half a brain would know you can never secure a border - but there are not many brains in Washington - those with brains know to stay away from Washington.
GPS has been discussed many times on this forum over the years. Never ever rely on the GPS to design the correct route. You must always check the route and put in waypoints to force the device to follow the route you want. No GPS can decide the correct route. It sees every road and every option and picks one. More often than not the route is not correct. We have had to design our own route by sometimes putting in as many as 10 waypoints along the way. Sometimes the GPS can get it right but we usually have to put in at least one waypoint. Our Garmin is greatly improved over previous versions but no GPS will ever be perfect because they will seek and find what they think is the shortest or fastest route. There is no way they can know this. You have to tell them where to go. If you don't very carefully check every mile of the route the GPS will be taking you on you could be going just about anywhere - and back again. I cannot tell you exactly how to use your specific GPS but Garmin does have all the manuals online where you can download and print them out. Then practice. You can use a Trip Planner I think they call it to design and save routes you will use again. You can save locations to use again. When you plan a route you put in your destination and then check the route. If the route is not to your liking you look it over and touch the screen at the point you want it to take you an then add that point to the route - when adding a point you want to zoom in on it and make sure you put it exactly where you want to go and also make sure it is not a one way street or some other reason for the GPS to refuse to go the way you want. GPS is a great tool and extremely useful but is does require that you tell it what to do. It is on electronic device and is not capable of reading your mind.
The Columbia crossing is on our GPS but we have the zoom in far enough to be able to see it - then we have to touch the screen exactly in the middle of the bridge or it will not know where to go - extreme zoom in. Our GPS will sometimes refuse to take the way we want to go - for example always want to go through downtown Laredo - you have to force it to go the way you want. It takes effort.