2006 Crown Vic transmission trouble

My 2006 police interceptor transmission was rebuilt 4000 miles ago... it had a hundred and eight thousand miles on it at the time it was professionally done at my friend's shop.... recently I was driving it at about 25 miles an hour when it seems to have dropped into first gear on its own.. I put it in neutral and pulled over... I was halfway to a wedding reception... it was the same distance to go home or to go to the reception... I proceed with caution and it seems to have started out in a higher gear... I took the overdrive off I presume... I drove about 25 to 35 miles an hour to my destination trying not to come to a stop... I can feel it slipping. Later I carefully got it home about eight miles distance.. it's now at my driveway waiting to go to my friend shop.. I have been researching troubleshooting... I have seen some YouTube mechanics speaking of RF frequency possibilities..... and which are African cities are leaking out of a coil or through transmission shift module.... causing erratic shifting...... maybe that was the problem before the transmission was rebuilt??? It may sound crazy or silly but does anyone have any possibilities of such information... no fly by wire gas pedal always seemed like it had a possible fault... overdrive seem to come in 3 or 4 miles an hour earlier than I thought it should.... anybody with any inputs...