Transmission, Voyager -95

I have a -95 Chrysler Voyager (Caravan) AWD with 149000 miles on it.

Posted here some months ago about my transmission problems, still looking
for advice.
Have the following problem:

When the car is cold, transmission works ok and just starting it up
and driving away it changes the gears perfectly. Now, when the car is
hot/very hot (let's say I stop and leave it idling until it's so warm
engine's cooling fan engage)
transmission then go crazy. When I put it into D it engages 1:st gear, but
when
it's supposed to shift into 2:nd it goes into NO GEAR AT ALL...and leave me
revving... (like neutral..but you can hear it sort of "trying" to engage but
nothing
happens.) At that point the ONLY thing I can do is to engage the Reverse,
(which works but with a clear "boink" when it engages.)
Now, if I switch the ignition OFF and start the car again it DOES engage
1:st gear fwd but that's
it...same thing happens all over again when it's supposed to go into
2:nd...meaning nothing...
(been turning the car off, starting up and driving home on 1:st gear (L) cpl
of times now to get the car home..LOL..)
When the car/transmission cools off, it works ok again until warm.

So, had a Chrysler dealer check it out and scan the tranny, and they
recommended
me to buy a rebuilt one (totalling over 4000$ with the installation! ...this
is Sweden..) as they didn't want to open it up themselves...
As I don't think the tranny is totally gone yet, I brought the car home to
think about it. The transcript of the scan says: P1784, "pressure switch
opened or closed at the wrong time". (I thought a tranny scan of a -95 would
give a two-digit fault code, but hey.. what do I know?...)

I currently have the car at a mechanic's and we're looking for more info.
Somebody told me there are plastic parts inside that can leak pressure (in
this case when warm)?

Information and experience on the matter much appreciated!

 

When the car was at the Chrysler dealer they tried replacing a solenoid
pack, but that didn't solve the problem...