Are the drive cups on the diff or wheel side worn out? The dogbones tend to 'eat' away from the cups and when this gets too extreme it will look like something is binding. The cups may look fine on the outside, but you may notice the inside to be worn out.
This weekend when racing I noticed odd behaviour in my serpent 710. When coming out of a corner full throttle it would seem like the right rear wheel was 'hopping', while when rolling the car by hand it was perfectly smooth. Investigating further, I found the drive cup on the wheel side was binding when under stress, actually pulling up the suspension!