I start driving my wife's 89 300E to work recently. The car has 95000 miles with a K&N filter and some aftermarket muffler. I notice the gas mileage on the freeway is about 20-21 mpg. Comparing to my friend's 93 400E claiming 25-27 mpg on freeway. I also notice when I cruise at 70 mph on freeway, the engine rpm is around 3000 comparing to my other 6 cylinders cars like 300zx and Honda Odyssey are about at 2000 rpm, Does this sound right? Any advise would help.