Poor acceleration and gear shifting, loud noise that increases with speed...

Hello, As for the poor acceleration, you will need a certified technician to find out why you seem to be lacking performance. The other two are related... most likely. When the car feels bouncy, you likely have worn out shocks/struts. When you have worn out shocks or struts, the tires begin 'cupping'. Cupping is when the individual tire treads begin to sit at different levels, so the tire surface is no longer smooth. It sounds like a truck with mud tires on pavement, and will get louder as you speed up, and never goes away. I'll leave you a link here for certified shops, so you can have your car taken care of properly. http://repairpal.com/nissan-within-10-miles-of-denham-springs-louisiana-70726