I believe the tire change made the ratio a step too tall. If it suits you, fine and good, but that engine will be a lot happier at around 2K RPM at 65 MPH, and 2500 is about where you'll get the best gas mileage. Just because you can hear the engine running doesn't mean it's over-revving. They were made to run wide open throttle all day at 3K or so while pulling a load without doing any engine damage. Lugging one down below 2K kills both gas mileage and performance. Ideally, a shift to the next higher gear in the transmission after achieving the HP peak in a lower gear should put the engine very slightly below the torque peak RPM.
Example: a 1958 235 cubic inch passenger car engine achieves its max BHP of 145 at 4200 RPM. Max torque of 215 Ft./Lbs. happens at 2400 RPM. A properly-geared vehicle with the right tires should max out in one gear around 4K, and after a shift, it should drop back to 2200 or so and be able to have close to 2,000 usable RPM's to pull in that gear. If the noise upsets you, I recommend a set of Caldwell noise-canceling electronic earmuffs from Midway USA. They're the same ones I use when running my chainsaw and shooting my .30-06.
Jerry
