I haven't been driving the Windstar as often, and I have not taken any pressure measurements, but I wanted to add some recent experience on this issue. The fault stopped occurring regularly in the first miles of a trip. The only thing that I thought had changed was going to winter temperatures. The last long trip I took in March did not have any occurrence of the P0741 code. Also, the more I see of this, the more I think the issue lays with either the PCM itself or the data that the PCM receives.
Note that these descriptions are for highway operation, usually interstates, usually on relatively flat terrain or sometimes in mountain areas.
-It is not related to transmission temperature... it will occur at just about any transmission temperature.
-If the vehicle is driven far enough after the code occurs, a code reset with resume normal operation of the TCC for the entire trip.
-It seems more likely to occur when driving in conditions that cause frequent TCC release/lockup cycles.
-I have seen the PCM set the P0741 code when my scan tool reported 100% TCC application (which should have locked the clutch) but the engine RPM did not fall to reflect the action of the expected operation of the clutch.
-After the P0741 is set, the TCC is disabled and the PCM does not attempt to lock again. The transmission oil temperature increases from ~170 degF to 300 degF when operating without any use of the TCC.
-After normal operation is resumed through OBDII code reset, the transmission temperature slowly decreases to the normal (~170 degF) operating point. If the code were related to the transmission temperature I'd expect it to reoccur when the temperature dropped back to normal temperature.
-The P0741 code has never re-occured after normal operation has been achieved. However if the reset is used too soon, the P0741 code will usually reoccur, but in different ways: (1) immediately on the first attempt to apply the TCC (2) immediately, but after the TCC was applied, RPM dropped as expected, and the code is reported when the clutch is released after the successful lock. The second style of error surprises me, since the code is reporting failure to lock, not failure to release.
-I have seen where the P0741 code did not occur over a period of multiple trips because a misfire code was stored from earlier malfunction of a fuel injector. Also, the P0741 fault began again as soon as the fuel injector was replaced and the PCM was reset. It seemed that the misfire code was able to prevent the P0741. I did not notice any inconsistency between the operation of the applied TCC and the engine RPM during the period when the code was not occurring, so I don't believe the fault was happening but not getting recorded.