I was going through the tour documents for the Jerry Garcia Band's November-December 1983 tour, which was unusually long. I haven't compared the various JGB tours, but this one and/or the late '77 tour are the two longest I can think of, without double checking.
The above is a rough map of the tour once the road tripping started, from Cleveland forward. (They had played 11/23 in Chicago and had Thanksgiving Day off, flying on Friday 11/25 to Cleveland.) I figure almost 3,200 miles on the bus, most of them (in the grey-shaded boxes) overnight from the previous night's show. So, on Friday, 12/2 they played the Tower in Upper Darby (outside of Philly), presumably ending rather late (they were wont to do that), hopped a bus for 300 overnight miles to Boston, played two shows, and hopped another bus 275 miles to Long Island, gigged at SUNY Stony Brook, and did 325 miles up to Vermont right after that show, enjoying a much-needed night off on Monday 12/5. What a hectic touring pace!
Again, this strikes me as exceptionally uncommon. They must have been in dire financial straits, or maybe it just seemed like a good idea at the time. I can't imagine how that bus must have smelled, nor do I wish to try.