2005 Aveo 5 poor mileage

[morpwr]

I see the graph of mileage vs speed, looks right. This is my first GM product in 30 years. I had a 2001 Suzuki Swift 1.3 litre 5 speed. it would get 45 -48 highway MPG. The Aveo is lucky to get 27-30. The RPM at 70 MPH is 3400. Is there a different year or vehicle that I could swap the differential or transmission 5th gear with, to drop it to 2500. The engine has plenty of power at 2500 to run the car along. Anybody put a K&N filter on, or a low restriction muffler with positive results. Any help would be appreciated. I like the car, but highway fuel economy is terrible for such a small car. Thanks Stephen

[wiseguydave]

I'm a new guy here but it sounds like your car is not shifting beyond 3rd gear (I had the same prob) In my case a re-learn procedure on the crankshaft position sensor cured it. Edit...I'm assuming you have auto trans.

[HeavyDuty]

Mine got 27 MPG hwy brand new in the summer time....does 28 now, with synthetic fluids/K&N filter/Iridium plugs/new 2012 throttle body/most recent PCM software updates installed and no a/c on....and both those figures are with premium fuel. When it's cold, 21 mpg. I did all this in the past 4 or 5 months was getting 23-24 mpg prior...I did get 31 once this summer on a tank right after all the above was just done.

Seems to me whatever I do the computer changes something to make it go back down LOL I should maybe change the other O2 sensor see what happens.

[petrified.rabbit]

you could get a diesel ? i think ? vauxhall f15? tranny in there. I forget the specs but there is one that has a taller final drive and an equally tall 5th gear. As well as one that has a taller 5th gear and an equal final drive (if thats your preference).