You know..Your problem could be something really simple..
Like not having enough Transmission Fluid in your Transmission..
Alot of people make the mistake of checking their Transmission Fluid with the car off..
Here is detailed instructions on how to check the Transmission Fluid on your 1996 Thunderbird..
Checking the Automatic Transmission Fluid
It is preferable to check the transmission fluid
level at normal operating temperature
150°F-170°F (66°C-77°C), after approximately 20
miles (30 km) of driving. However, if necessary,
you can check the fluid level without having to
drive 20 miles (30 km) to obtain a normal
operating temperature if outside temperatures
are above 50°F (10°C).
With the vehicle on a level surface, start the
engine and, while fully applying the brake
pedal, move the transmission shift selector
through all of the gear ranges allowing sufficient
time for each position to engage. Securely latch
the transmission shift selector in the P (Park)
position, fully set the parking brake and leave
the engine running.
NOTE: Your vehicle should not be driven if
the fluid level is below the low cold
reading on the dipstick.
Wipe off the dipstick cap, pull the dipstick out
and wipe the indicator end clean. Put the
dipstick back into the filler tube and make sure
it is fully seated. Pull the dipstick out and read
the fluid level.
When checking fluid at normal operating
temperature 150°F-170°F (66°C-77°C), the fluid
level should be within the hot notched area on
the dipstick. When the vehicle has not been
driven, and the fluid is at room temperature
50°F-95°F (10°C-35°C), the fluid level should be
within the cold notched area.
NOTE: If the vehicle has been operated for an
extended period at high speeds or in
city traffic during hot weather, or
pulling a trailer, the vehicle should be
turned off for about 30 minutes to
allow the fluid to cool before checking..
Courtesy of TheTerminator93