Did you just get this coach and notice the problem, or have you had it awhile and now the problem has developed?
U-Joints work well, only when they're pretty close to straight-on. When they have to accommodate quite a bit of angle, they accelerate and then slow the shaft. That's why modern FWD and 4WD vehicles use CV (CONSTANT Velocity) joints instead of U-Joints.
Point of this is, you need a little "off angle" for the driveshaft to NOT oscillate as if it was one long shaft. But not too much. I helped a member here with some angle measurements, and it turned out the front flange on the differential was too vertical. Rear axle needed to be shimmed so the flange came closer to the angle of the driveshaft.
All said, the Carrier Bearing(s) are big ball bearings that can go bad, but often the rubber mounting breaks down, and you get vibration.
If God's Your Co-Pilot Move Over, jd
2003 Jayco Escapade 31A on 2002 Ford E450 V10 4R100 218" WB