Our experience is similar.  Driving 67-68 mph on a 65 mph highway you get passed like you're sitting still.

Once we had to get to a soccer meet to deliver something and because it was a hurry up deal I got behind a car going 80 mph.  After  a couple of miles we were both passed by somebody just as if we were going 65.

Many years ago a friend and I were returning from Florida and as we were heading to Nashville we were getting passed constantly.  We were in a 396 Camaro and my buddy decided to keep up.  We ended up running 125 for a while and as cars exited  the highway we laughed as many of them were blowing blue smoke.  No idea if it's still the same.

America's Autobahn is I80, US30, US61 and probably a lot others.