2000 grand marquis-70,000 miles- while driving car will abruptly downshift- as this happens the heat sensor light will flash on- thiis has happened several times over last month- a short interuption and car has proceeded as normal- yesterday this happened and it was more then a split second - the car actually died and most dash lkghts flashed- car restarted and worked fine- I have driven this car and the trans seems to work fine- down and upshift - I feel this may be an electrical or computer problem - any help out there?

When's the last time you changed your tranny fluid???

First, (with the engine OFF), Disconnect the NEGATIVE battery cable. Then disconnect the POSITIVE battery cable.
Make sure the battery is fully charged and the battery (distilled) water is at the correct level.
Leave the cables disconnected for one (1) hour.
Reconnect the battery, POSITIVE cable FIRST; NEGATIVE cable LAST.
Start the car, drive it for 10 miles, and check the transmission fluid.
The fluid should be BRIGHT RED, and filled to the cross-hatched area.
If the fluid is NOT bright red, it must be changed (NOT "flushed!"), and the internal filter and the inline filter must be changed , as well.
Fill with Mercon V fluid, and DO NOT OVERFILL !!
Good Luck !!