My car has about 3000 miles on it now. I've been averaging about 63 - 64 MPGs in normal conditions, which includes passengers, air conditioning etc. Lately, even in the best of conditions I can't seem to average more than 60 or 61. I'm not doing anything differently except NOT running the air conditioning. It seems that my display changes more often than once per minute when in city conditions and that it can drop from 65 to 60 within a mile or so of city driving. What am I doing wrong? This should be increasing rather than decreasing? (even though I know that this is still very good).