I traded my 2002 Dodge Grand Caravan (3.3 V6) about a year ago for a 2005 Dodge Grand Caravan (3.8 V6). On long trips, I could get about 320 miles out of a 20 gal. tank of gas before I was red-lining with the 2002. On the 2005 Grand Caravan, I've gone about 420 miles before red-lining (20 gal tank). Is this due to the motor 5W/20 motor oil? I used 5W/30 in the '02.