I have the same problem on my Merc 97 LS 24v6.
The fault codes are 1742 and 1744. I had a conversation in the local
independent transmission shop and they said *presumably* it can be fixed
with no overhaul of  the tranny. The best case scenario - just a
replacement of the solenoid controlling the TC.
Then the parts + labour price would be about 350-400 Cdn.
If I am a less lucky then some tranny valves would need to be replaced
at about 900 Cdn (parts +labour). The local Ford dealer asks a way more.

Be prepared the car stalls on a stop signal or on lights.
You can start again by doing this:
1) Put clutch to N an start the car
2) slightly press the gas pedal Up to 1500-1700 prm
3) release the gas pedal and immediately shift to D
4) slightly press the gas pedal again.

The car will make a jump and start moving.

Of course this in not a good way to drive and you use it only in the
cases when you really need to do it . Otservise there will be dfferent
figures on the repearance estimetes.

DNB