ok my moms car is a 97 acura 3.2 tl without premium package. it have about 70k on it and was recently purchased. no papers from checkups are in the car. when she is riding on a highway for about 30 or 45 mins the car starts to shake and when she lets off the gas it starts slowing faster then normal. it kinda makes a knocking / scrubbing noise and her trans. fluid is fine right on the mark. just wanted to get some input on the subject andwhat you think it might be.

 

There could be so many things. You will need to narrow it down a little more. Also, if it was recently purchased, why not bring it back to the place where she bought it from and let them check it out?