Q: Engine still rocks back and forth. What can it be?

If you are using aftermarket mounts, that introduces a bit of a complexity in diagnosing a problem such as this as aftermarket parts can always be a potential cause of fit and function problems after installation. The only way to guarantee a "baseline" against which to measure, in this instance, engine movement is to use the original design OEM, Nissan supplied parts. If you have those parts installed at present, and you still see movement, such movement might be within the range that is expected as there will always be a degree of movement in the engine on acceleration and shifting. To advise you further I (or any mechanic) would have to know if the mounts are OEM and, as well, see in person the exact extent of the movement that exists. If you want the required diagnostic steps performed by a certified Mechanic, dispatched by YourMechanic right to your location, please request a motor mount inspection/diagnostic. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.