Panics right, but you might try backing into it. Find out at what RPM you get your best mpg now. This won't take into consideration wind resistance, and since your going to be slower your mpg will improve anyway, but there might jump. My 68 has a Quadrajet and if I keep the RPM under 2500 my mpg jumps from 8-9 to 10-12. I went from 4.56 to 3.73 it helped but I'm still over 2500 at 65 mph. Running the numbers rear axle ratio, tire size, on an RPM calculator will tell you what ratio to get to stay at your best RPM. On my 68 I would have better mpg with a 3.30 or 3.42. Hope that helps.
An overdrive would be the solution.
Larry
