Towing steep inclines, brake fade, proper braking

Yeah, Google Earth elevation profile is a work in progress. I suspect the very short sections of excessive grade (the little wiggles) are due to errors in the ground elevation at different points along the route. Yes, maybe it has to do with the road cuts and fills. When I run a route from Coos Bay, Oregon to Mount Shasta City, California, it doesn't show any obviously erroneous grades. So the results will of course vary with the particulars. But it is kinda fun to play with.

I've noticed another strange thing. Sometimes the close up view of a bridge shows the roadway surface of the bridge laying on the river-bed below. Yes, a work in progress.

I tried the same route and also noticed some very strange (steep) grades. But when I zoomed in on the area with these anomalies, it is in the location of the Eisenhower Tunnel. Evidently Google Earth is using ground elevation (the mountain above the tunnel) to calculate the road profile. So I would just ignore the results for the portion of the route in the tunnel. Using Google Earth you can easily determine ground elevation and geographic coordinates - just point the cursor at the location of interest. There isn't a tremendous elevation difference between both ends of the tunnel. The ends are at 11,186 feet and 11,075 feet, just a 100 feet difference. Using the "Tools - Ruler" utility the straight-line distance between tunnel entrances is 1.72  miles. So the average grade in the tunnel is not severe.

So you didn't do anything wrong, Charlie. Google Earth doesn't deal with tunnels correctly. Maybe they will get the problem fixed in the future. In the meantime we'll just ignore grades shown in tunnels.