08R320CDI

Had a chance to go for a good drive today, and noticed that when the dreaded shuddering would occur (sounds like driving over a rumble strip at higher speeds, and more like a washboard surface at lower speeds) the tach would go up a few hundred, the shudder would manifest, then the revs would drop back down. Any suggestions? I know about the rubber disks between trans and driveshafts, but those still look to be in good shape, no strings hanging out, no degradation to the material at all really. What else should I check?