Trans fluid may thin a bit, but it also expands when hot. As far as the vibration, just remove some of the fluid through the dip stick filler tibe. Get a rubber hose long enough to reach all the way down the tube into the trans. Then just get something that will create a vacuum that can be hooked to the hose and take fluid out. This is the easiest way to remove fluid otherwise you will need to remove the pan which means you loose all the fluid in that area (about 4 qts.). That way you'll know if the fluid is the cause.
I don't think it's causing a vibration, but one never knows.
Let me know if this helps or if you have other questions.
Saturday, December 20th, 2008 AT 2:30 PM