I second that and was very impressed, not only with the engine and
car, but the result.  Last May I flew to Salt Lake City for a couple
days, then rented a Cadillac Deville (big car) to drive to Reno and return.
  Being a bit intimidated by this behemoth, as I've never even sat in a
Cadillac, I nursed the thing around SLC for 3 days.  Oddly enough, the
dash readout initially, was in Metric and I couldn't figure out how to
change it to Decimal right away. (There was no owners manual in the car)
  The mileage on the trip computer said 10 litres/100 kilimeters, which
translates to around 18 mpg+/-.   I figured that wasn't too bad,
considering the gas prices.  By the time we set out westbound, we
corrected the readout to decimal.  Heading for Bonneville on Rt 80, we
nursed the car along at 60-65mph, taking in whatever sights came along.
 The trip computer started to indicate higher mpg.  To my astonishment,
by the time we neared Wendover, it was reading 31.2 mpg.  I checked the
instantaneous mileage on the trip computer and it was bouncing around
34-36-29, etc.  This was backed up, by the fill up at Wendover.  It only
took 3+ gallons. Amazing!  I think this is the best kept secret GM was
ever foolish enough to keep.   On the return trip, weeks later, I threw
caution to the wind and ran around 75-80, again achieving around 28mpg,
which in a 4500 Lb car is exceptional.
  Unfortunatley, though,  regardless of the great mileage and creature
comforts, I could never bring my self to buy a GM car...