About 10 months ago, I noticed a fairly precipitous drop in gas
mileage in my 2001 6-cylinder Automatic Rodeo, from the 18-20 mpg
range down to about 11-12 today.  I'm not 100% sure if this was an
overnight thing, or something that happened over time (my wife is the
primary driver of the vehicle).  I've taken it to 2 mechanics, both of
whom don't know the cause.  Several people have mentioned the
increased use of ethanol in gas today.  I use Regular Gasoline all the
time (87 octane).  Couple of things I've tried:

- Only put 10 gallons of gas instead of a full tank - no effect.
- Run the car without A/C (1 mechanic thought it may be some kind of
drag the A/C system was putting on the engine(???) - no effect.
- 1 tank of 93 octane gas - no effect.

I did notice that the car goes about .95 miles for every mile the
odometer reads...so, that would do some damage to my perceived gas
mileage, but it doesn't account for the roughly 40% drop I've noticed.

Has anyone else had this problem?  Any ideas?  Fuel additives, or more
regular usage of higher octane gas?

Thanks!