I have a 60 gallon gravity transfer in my truck. LOVE IT. I haven't really calculated it but I think a can go 1200 or so miles..
I filled up in Sonora, drove to Lubbock, picked up another hunter, drove to Cloudcroft. Drove around the forest the next day, probably 40+ miles or so. The rest of the hunt a was in another vehicle. Drove to Artesia, to Ft. Stockton and was about 10-20 miles east of FT Stockton before my needle started to move. I use to have to fill up every other day to every couple, if I was hauling livestock I may have even had to fill up after the load. Now I have to remind myself to look at the gauge every once in awhile!