Strange vibration when holding at 50 MPH?

When holding at 50mph in top gear, 2k rpms, there is a shudder as if you're driving over a washboard road. I think it's up front but can't be sure. Inspected all 4-wheel bearings and suspension and steering components. Driveshaft U joints are okay. Right side CV axle has very slight play. In all other gears holding at 2k there is no vibration. If you accelerate quickly from a stop the transmission shifts fine, albeit high rpms, 7k-8k well into redline, and the engine sounds strong with no loss of power or vibration. When it occurs if you let off or accelerate slightly it goes away. I had another 2003 CRV that had a similar issue, but the left side inner CV boot was torn, and grease had leaked out. Never repaired it. I've heard this is usually the right CV axle and a common problem with aftermarket axles. The only suspension components in question are the rear end links but I don't believe they're the cause.