[Bill Eveland]

Most or just about all the first order vibrations I've dealt with (one per revolution) occur at lower speeds, usually 45-55 mph. I would say at higher speeds you could have other issues. If you can get a sirometer and hold it againt something solid on the car you can get the frequency and find the rpm of the vibration . First order driveline vibrations are 25-35 HZ or up to 45 hz which is a driveshaft speed of 1500-2100 rpm depending on wheel speed and ring gear ratio for driveline speed. Here is a chart from a Ford tsb that has a little info that may be usefull.