[Esajuppeli]

I have 1992 Audi 100 CS quattro. EPA ratings are 16mpg for city and 20mpg for highway. I usually get 17-20mpg in city and 23-25mpg. My all-time average is 19.3mpg (60% city 40% hwy). Best trip was 28.0mpg (180 miles with 2 persons, a dog, about 150lbs of luggage, 45mph average speed).

I'd like to get my average over 22mpg and 45mph average trips over 30mpg. What should I do first? I've done all general maintenance and blocked a part of radiator because of cold winters here in Finland.

Specs:
2.8 V6, done 203000 miles
4spd automatic gear box with TC lockup on 3rd and 4th gear
4-wheel drive
0.32cd
~3400lbs curb weight
98E5 fuel (USA "93" with 5% ethanol)
Original 15" wheels with 205/65r15 studded tires