FordPhD

99 Explorer Limited AWD (current odometer: ~78000)
Before service: Average MPG was 16.7
After Service: Average MPG is 14.5

Tire pressure checked.
Driving condition: Same.

Services as follow:
1. New oil/filter: Mobil 1 5w30
2. Transmission service (new filter/gasket/fluid)
3. New Transfer case fluid
4. Power steering flush/new fluid
5. Radiator flush/new antifreeze/thermostat (same)
6. Brakes service (new pads)
7. New K&N air filter
8. New lockable gas cap

Can anyone possible give me any reason(s) why my MPG went down?

thefonz

From what you changed, the only thing I can think of, is with the new brake pads. If your caliper isn't releasing properly, possibly putting a little 'drag' on the car.
Was the K&N air filter just a filter replacement, or a whole new filter system installed?
Are you buying the same grade of gas and at the same station?

FordPhD

Same gas station & same grade. K&N is a filter replacement (nothing special). Brake pads were actually serviced prior to other services (before the drop in MPG).

rervf23

Is it possible that this is a coincidence - maybe the gas stations in your area have switched to the winter formula gasoline. That will cause a drop in your mpg.