I have an early a604 (around 1989) that came out of a Dynasty originally and it goes forward in all selections, even park, well sorta. It tries to go forward in park but the park pawl won't let the car move. R, N, D all go forward. Any ideas? I suspect the solenoid pack but am not sure.
Thanks.
-Chris

 

Welcome to DF
Have you had the transmission ck for codes? What may have happen is the a couple of clutch pack have weld together,causing the transmission to move forward. It maybe time to do a tear down or replace the transmission.