Drove from Mississippi to Seattle. That took roughly 36 hours over 4 days and 2700 miles(the highways/bypasses made it very easy to speed).
I remember almost running out of gas in Montana as we were in the middle of nowhere. Add to that it was pitch black, so I was sweating bullets. Luckily, we found a gas station with about 15 miles left in the tank.
It was some of the most beautiful scenery though. On the way back we took the Pacific route and went through Oregon, California, Nevada, Colorado. Those were some of the most beautiful places I've ever seen. The return trip took six days and was closer to 3000 miles. Definitely recommend driving across the US if you have time for it.