No more iac (idle air contol valve).
Drive by wire. Throttle position determines idle speed. (great for traction control)
I don't even pay attention to customers with MPG concerns. (Toyota)
RARELY does anyone DOCUMENT their mpg.
The ECM's are very sophisticated, and would know if something was amiss.
What has the weather and temperatures been like for the past several months?
Have the fuels been reformulated for temperature changes?
Has E85, or oxygenated fuels been in use??
Are you the only driver? More traffic than usual, Driving faster??
Do you now warm your car up on cold mornings,maybe to deice??
All these things ,and more, kill mpg.