transmission was not shifting well from 1st to 2nd and 2nd to third?

I would scan the car for codes first because it sounds like the ECM, or the input shaft speed sensor is not working. Here is a guide to help you get the codes and the location of the sensor in the images below.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing


Check out the images (below). Please let us know what happens.

Well, it has been a couple weeks and the problem still exist. Here's the update: The transmission has been replaced twice, and both transmissions, along with the original transmission all have the same problem I described above. The Error code that is given from all three transmissions is P0746 which is the pressure control solenoid.
Since the transmission has been replaced twice and I still have the same error/problem, I'm thinking the problem lies elsewhere. But where or what should the mechanic look at next? He told me he tested the solenoid and wire continuity, and it was all okay. I've already spent more money on the car than I paid for it.
Your help is greatly appreciated.

Here is what is said about the p0746 code:

The P0746 code is related to the operation of the transmission in an automatic transmission-equipped vehicle. Specifically, it indicates that there is a problem with the Pressure Control Solenoid "A" Performance.

So, if the code is still there and the wiring is good, I would replace the ECM. Here are the location and instructions in the images below. You can get a preprogrammed unit by searching Google or Ebay. Check out the images (below). Please let us know what happens.