My 01 grand prix 3.8 L won't shift right. You can keep keep it in park and rev it to 3000rpms and it will start to shake. If you are driving it you get to about 10 mph and it shakes until it decides it wants to shift. If you let off the gas just a little it will shift. You can't really go faster than 40mph. It feels like its shuddering at about 2000 rpms. I don't think its the transmission because it still does it in park. Any ideas?