Boston to Seattle on a train (around 3000 miles). It wasn't bad at all. I'd do it again if the opportunity came up.
Did you take Amtrak? Cuz i looked it up, and from Boston to Seattle it was about 60 hours.
CBA to find the exact milage, but I just got off of a bus ride from Palenque to Merida. That was about 2 hours ago and it was 8 hours total. Probably too far.