Wow! I am so glad I found this thread! I am planning on doing almost the same thing in June. We are planning on trailering the bikes across the country to my wife's cousin's place in Riverside. I don't want to drive as far east as El Paso, but otherwise the route is about what I was thinking of.
I'm concerned about range too. My bike holds 5 gallons but I usually only get a little over 100 miles before the fuel light comes on. I guess I could get to 130 or so before running out. Will I have to carry gas in cans? How much range do you need to safely drive a route like this?