Own a 2000 century with 86,000 miles. Have a vibration thru the car between 45 to 50 mph. Rotated tires same condition. Checked steering (tight) and motor mounts look good. Serviced transmission recently. Pan was clean. Have not put on scanner yet. Local shops around here charge a lot. Any thoughts on what to look for next?

One of the rims or tires may have issues. How old are the tires?
Have you had all 4 wheels on a good balancing machine lately?

I would agree, that sounds more like a potential wheel balance issue than transmission or anything that would need a computerized scan... depending on the type of vibration. Unbalanced wheels will start to become evidence at higher speeds. Can you tell if there any "wobble" to the vibration, or is it more like a loud "buzzing" sensation? Those are the best words I can think of. Feel free to describe it otherwise if you can!

If you had the tires/rims mounted & balanced somewhere recently, drive back in and ask them to re-balance the wheels. If your wheel weights (small curved metal pieces, hooked into small brackets on the edge of the rim) are on the outside as most are, also check and make sure none of them flew off.

Are we talking a vibration, or a noise?

Does the steering wheel shake?

Or is it more a growling noise from the bearing?

Heh, much better descriptions there than what I called "wobble" and "buzzing". Thanks.

Several months ago, my van had a wobble/rumble at around 40-50 mph.

Without looking, I thought it might have been loose lugnuts - just had some tires replaced. Nope. Took it back to the guys who put the new tires on the front, they said the left rear had separated.

Turned out there was a current recall on that (Goodyear) rear tire - they didn't catch it when it was in for front tires. I got two more (rear) Goodyears at no charge - courtesy of Goodyear.