98 avenger question

I had a used transmission automatic into my 98 avenger. The mechanic said the car would need to "relearn" shifting. Is this something to do with the ecu? It shifts hard going from first to second and second to first. The whole car shakes. He said driving it might help. It does seem like the tach goes up alot higher before it shifts then I remember. Also it seems like the gear shift is sloppy. Every automatic i drove that had a floor shifter always clicked into gear. This one clicks but it feels mushy. Sometimes if you don't get the shifter down all the way into drive it will slip upwards into neutral. Anything I can do?

The shifts might need to relearn themselves. When the ECU is reset the car will idle weird, shift weird, etc, until it relearns parameters.

The shifts might need to relearn themselves. When the ECU is reset the car will idle weird, shift weird, etc, until it relearns parameters.

Is this something it does on its own?

It is something that will be adapted over time, but if you can find someone with a professional scan tool, you might have them reset the Clutch Volume Index values for the transmission. Chryslers of that era had a CVI parameter for each of the clutches which in general terms means the amount of fluid pressure required for each clutch to prevent slip. If the CVI parameters in your car's ECU are still set with what the worn/failed transmission required, your ECU may be trying to use really high pressures to with the current transmission. I'm not positive these CVI parameters would have much of an impact on shift harshness, but it seems likely they could since it may engage the clutches more rapidly and therefore cause the harsh shift.

-Rod