2000 Mitsubishi Mirage starts to shakes at 50mph what could this be?

OK i have a 2000 mitsubishi mirage. When i get to about 50 mph it starts to vibrate which makes it feel like something is knocking in the engine. When im in the penger seat i can feel it alot...but when im driving it is mainly under the gas pedal. It also goes to the right when i slow down. I was told it could be my motor mounts, tire balance, harmonic balancer....and a few more. When i am coming to a stop from a high speed...once i stop the front end shakes real bad but just for a second.