Holden Commodore 2009: Locking up early

My 2009 six-cylinder VE Commodore Omega drops into lock-up top very early, sometimes around 60-70 km/h under light throttle on a flat road causing an annoying vibration as if the drivetrain is under too much load. Switching into Sport mode is much better except it then probably doesn't lock-up at all around town. A Holden service manager said the only fix was a software upgrade which GM has developed, but if you do that then it won't lock-up until about 110 km/h. Is this issue normal for this model or would resetting the computer improve things?