DO NOT FLUSH THE TRANSMISSION!!! Doing so seems to lead to problems. I have changed both my VX's to Amsoil Synthetic with no problems, one at 103,000 miles and one at 150,000 miles, but I sure as heck did not flush them! A filter change can only help...

Yes our transmissions are four speeds, what you are most likely sensing is the torque converter locking up at speed, that would be normal...