viberating 97 ranger

Hello,I'm new to this forum and am hoping someone can help me. I have a 97 ranger ,it starts to viberate at around 57 mph and starts to mellow out around 65mph or so, it's not shaking,just a smooth viberation like one of those back massagers,I don't think it's in the front,more like the drive shaft or something with the transmission and it seems to be getting worse. Thank you.

When was the last time you had the wheels balanced? Sometimes an out of balance wheel only shows itself at certain speeds. If you have a slight bulge in the tire it might only contact the road at certain speeds.

I would also take a look at the tranny mounts and rear wheel bearings. Something getting louder is usually something that's wearing - a wheel bearing might do that, but it's usually a more continual noise.

When was the last time you had the wheels balanced? Sometimes an out of balance wheel only shows itself at certain speeds. If you have a slight bulge in the tire it might only contact the road at certain speeds.

I would also take a look at the tranny mounts and rear wheel bearings. Something getting louder is usually something that's wearing - a wheel bearing might do that, but it's usually a more continual noise.
I would suggest checking the u joints on your rear driveshaft. Ive had to replace mine a couple of times. City driving is especially hard on u joints in trucks.