2004 Subaru Impreza Reved too high too cold. Engine now kno

About a month ago I revved my engine a little too high when it was probably way too cold. Ever since then my engine's performance has gone downhill. It starts fine, but as soon as I give it a little gas it knocks then goes into it's normal sounding rev's. However as soon as I put it in gear and start to drive the car shakes and is slow to go, I have to give it a lot of gas. Also when it's sitting idleing the car is fine when it's cold, but as soon as it heats up the whole car starts to vibrate. Also I just took a trip my mileage used to be about 35 mpg, I could go from regina to swift current on a full tank and end with just under 3/4's of a tank. This last trip took 3/4's of a tank to get there. Anyone have an idea of what it is? I know it sounds expensive, it also has aftermarket venom injectors. And a larger turbo.