How to increase your sight reading ability?

Hey, so I've played piano for about 5 years now, I can sight read violin (played for 8 years) like a beast, and can sight-read tenor part like a beast. Haha, not bragging... just saying I've got that down. Anywho, in piano, I feel like I've gotten rather good at emotion and all that jazz, but I feel like the only thing holding me back is my sight reading in piano! Putting both of the clefs together! It takes me a while to learn a piece, and most of the time I just memorize the part and practice it over and over till it's ingrained in the early stages. I would like to be able to just play through music! My teacher said you just have to literally do that--just run through music. Can anyone add to this? Any techniques or methods that have worked for them? Thanks!