2001 Sable Convertor Hunting

While driving my sable at a cruising speed, the torque converter is unlocking intermidently on a continual basis.... I'd say every 15-30 seconds the convertor will just unlock for a brief moment and then lock back up.... even while on the freeway at 75 mph.... Trans works fine no other symtoms but I'm worried this is going to wear the clutch in the convertor....

Any ideas?