Until the post about the directional data, this sounded much like my post here..
http://www.chiefdelphi.com/forums/sh...ad.php?t=94497
Could be digital sidecard power short.. with the directional data, I would agree with checking the jags individually. We have had 3 jags fail this year in one direction. The error indication on the jag is a flashing red led, that can easily be mistaken for the normal, jag running backwards proportional flashing red. I know you said when the robot forward, but many times robot forward, is jags reverse.
We have 2 motors per side on a 6 wheel tank drive, and when we lost one jag on a side, the drivers really didn't notice it, but autonomous did. Also in the semi finals at MSC, we lost a drive chain, the drivers did not notice it until we were off the field, and only when battery hold down bungee was cut by the chain saw..