2003 Holden Commodore VY Crewman shuddering under acceleration

This could be the result of a worn or poorly adjusted transmission, a worn torque converter or even something simple like a low transmission-fluid level. So that’s job one: Check the level of fluid on the dipstick. If that’s okay, you really need to see a transmission specialist who has probably seen these exact symptoms before. What I can tell you for sure is that the automatic gearboxes fitted to Holdens of this era did have a finite lifespan before they needed either an overhaul or outright replacement.

But make sure your mechanic checks that the cause of the vibration is not a worn universal joint or bent axle or an out-of-balance drive-shaft. Even a sticking brake or a worn engine mount can induce vibrations into a moving or accelerating car, so rule all that stuff out first.