1999 Chrysler LHS Question: Transmission does a sudden downshift
 

While driving, the car just does a sudden downshift, like it goes into limp mode for a second then continues on as normal. It happens at random times. What I can tell is that when it happens no dash lights come on, the tach goes up and the speedo drops down some.
Dealer said it had active code p1739-tcm power up at speed
I have replaced cam sensor,crank sensor,speed sensors etc
I put in a used tcm and car ran fine for about 200 miles and now it is doing the limp mode thing again.
Car has about 158,000 miles
Any ideas?