addicted to efficiency, unexpectedly

my car has figured out that gas prices are high.  he's spontaneously become 10-12% more efficient with fuel.  in the last 2 tanks (2 months), we've had some crazy good gas mileage.  i can't figure it out.  it's not related to tire pressure (which used to be bad but has been good for 18 monthts), it's not related to driving patterns (which have changed little in the past 9 months), and it's not related to fuel or weather (which are nothing he hasn't met before.  i thought maybe it was because i've been driving at lower speeds because he's presenty illegal/unregistered, but i haven't been any more careful than i was before, when i was trying to chase those 4 tickets off my record - and "cautiously" on the east coast is still 15 mph over.  so i can't figure it out, other than he's the best sentient vehicle ever.  and that includes kit.