I recently purchased an '08 C70. There was shuddering under acceleration so I replaced the spark plugs and checked the coil packs by disconnecting each one in turn. They all caused a drop in RPM. Then I replaced all the motor mounts and both axles. This cured most of the shudder problems but there is still a slight shudder under heavy acceleration. I'm at a loss as to why I still have problem. Could the torque converter be starting fail, weak coil packs, ect?

 

I have the same issue. After having eliminated the likely causes, the last thing for me to try is replacing the auto trans fluid as I've read reports of that being a possible cause. New oil and filter are sitting in my garage, waiting until I can get to it.

 

Thanks for giving me a possibility to check out.