1) the gas smell ??? No clue there on that one 2) the rattle...does it sound like it's coming from the dash around the Radio, or from around the ash tray. if it does, it is most likley the bushings in your shifter. This happened to me when I installed my new Gears, and we cracked one of the shifter bushings reinstalling...it was very annoying, at just the right RPM (right around 3000), you would hear a rattle coming from the ash tray area..
Also...is there ALOT of play in your shifter from Side to side...if so, I think we found your problem
hope this helps