Install a tack and judge rpm by that as opposed to sound .
A number of years ago I did a 600 mile day trip at 60 mph at 3000 rpm . The truck ran fine and required no down shifting on the larger hills as it did when I had an over drive trans. I even had a little better gas millage than when doing 60 mph at 2200 rpm . In time I realized that the motor seems to come alive at about 2500 rpm and starts to drop of at around 3000. I'm not a mechanic and any tuning I do is by ear and I sure guess a real mechanic could get it to perform better , but they still need to rev.
John
