Ideal Speed In Class A Gas MH

I drive from 50-70 mph depending on road conditions and traffic. I drive more by rpm and my vacuum gauge than my speedometer. Each engine has a max torque and HP rpm. My best mpg is at the highest vacuum reading which makes it easy. So mph will vary with hills and head winds. I know what reading the MH will down shift so if I see a big hill I might hit 70 at the bottom and let off the gas as I climb to keep it from downshifting. In general the best mpg is in high gear when vacuum is over 10 ins of Hg. Out west with no or little traffic I can ave over 9 mpgs easily. Over 80k miles of travel I have average 8.7 mps. Headers, FF mufflers, CAI,and advancing the timing added much more HP and performance but did not help mpg. Driving by RPM and vacuum did.