well i dont have a ls but i have the same engine and i got about 310-320 per 11 gallons. and for the window ratteling you might want to tighten up somethig inside of your door and for the passenger side slowing down like that its probably because there is crudd on the track of the window soo take the door panel off and either just stick some oil in there or if its too dirty then just go ahead and clean it up