I have a 2008 maxima with 103000. I just replaced the cat based on code P0420. I still get a vibration that I feel in the gas pedal on slight acceleration or uphill between 65 mph and up. It feels like the car is running on 5 cylinders. Put the car in neutral at that speed and its smooth. Lower speeds is fine. I was told by my mechanic that he saw a code P0868. Im not worried about that because of Nissans extended tranny warranty. Problem is that the dealer doesnt see that code anymore. Dealer says I have a weakend upper and lower front motor mount.
My question is what is causing this vibration. Motor mounts or tranny?
Any help would be appreciated. I love the car but dont want to do a trial an error on fixing vibration.

THanks in advance for ANY info.