It sounds like the kickdown linkage return spring became disconnected. The linkage is a spring-loaded link that is pushed with the accelerator pedal and it controls when the transmission shifts.
Photos of the linkage for your model seem to not exist, but the design is the same for all older Chrysler models back to the 1960s. This first photo shows the linkage you should find near the center of the engine compartment after you lift the hood. On these older cars the linkage got pushed rearward and the spring pulled it forward. On your car, the link gets pushed toward the driver's side, and the spring pulls it back toward the passenger side.
The blue arrow is pointing to the end of the linkage. It is at its "at-rest" position due to the spring, (red arrow). In the second photo, the linkage has fallen halfway back because the spring is broken or disconnected. That spring is rather long, but it is not terribly strong. Once reconnected or replaced, you will be able to push that linkage in the opposite direction the white arrow is pointing, with very light thumb pressure. The system will work fine with a very strong spring, but you're pushing against it when you press the accelerator pedal. Too strong of a spring will tire your foot very quickly.
When you accelerate, the timing of the up-shifts is delayed depending on how hard you're accelerating. This linkage and road speed are the two variables that determine when a shift occurs. When the spring is missing or broken, the weight alone of the linkage is enough to cause it to go to the position shown by the pink arrow. In this case the transmission incorrectly thinks you're pressing the accelerator pedal down further than you really are, so it waits until a higher road speed to up-shift.
This spring has a very low failure rate, so you should be able to find one in any pick-your-own-parts salvage yard. If all that happened is the hook broke off, you can bend a new one and just reuse the old spring.
I would never say this out loud, but a couple of larger rubber bands tied together end to end will work for a temporary fix to allow you to drive to the salvage yard. There's a real good chance you can find a new spring at an auto parts store or hardware store as they usually have somewhat universal springs that will match pretty close.
The clue to this problem is you're going to find the up-shifts occur always at the same road speed, regardless if you're accelerating very lightly or you have the pedal to the floor.
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Wednesday, February 22nd, 2023 AT 2:04 PM