That you for the info. I will let you know how I make out with the tranny. Salvatore.

Better fuel economy can be acheived by turning off overdrive until you reach approx. 65 mph on the freeway then turn the overdrive back on again. It should be easy to remember just turn it of every time you shift into gear.

The default position for the Overdrive is "ON!"
There is NO WAY that turning the Overdrive "OFF" will improve your fuel economy on the FOMOCO 4-speed Automatic transmission.
The transmission is controlled electronically, and knows exactly which gear it should be in according to the engine speed and load.

Your had your transmission "flushed out". After doing so, your fuel mileage decreased noticeably.
Problems such as yours are the reason why you should NEVER FLUSH the Grand Marquis transmission !!
The "Tranny Flush" is a way for Dealers and Shops to make money very quickly by eliminating steps in the "Transmission Service" procedure.
They win, YOU lose !!
Your Marquis' auto transmission is properly serviced by removing the transmission pan, cleaning the internal magnet, changing the internal filter,
and drain & re-fill the the Torque Converter.
Trans Pan Gasket is RE-USABLE, and requires NO SEALANT.
The complete job requires 12 quarts of MERCON V -type trans fluid and a MotorCraft (OEM) transmission filter.
The Motorcraft filter comes with NO gasket, so the original gasket is cleaned with WD-40 and re-used.
If your original gasket is damaged, replace with MotorCraft gasket ONLY !! NEVER use a cork gasket.
Changing the Trans Filter at 35,000-mile intervals is all that's necessary to keep your transmission shifting smoothly and without slippage.
If appearance of the trans fluid is bright red, and has no "burnt" odor, it's not necessary to drain the Torque Converter at every filter change.
For those who do their own work --
When trans pan is off, it's a good time to install a B&M Drain Plug Kit -- saves work and messy cleanup on next filter change.
For snappier shifts, I installed a B&M Shift Improver Kit, and for long life, a B&M Transmission Cooler.

A 15 year old thread from the dead.