Check engine light is on and codes P0700 and P0731, reverse is not working and van is in limp mode

Have changed 4 sensors, 3 of which rats had eaten through, also changed the shift solenoid and TCM. Runs okay until I put it in reverse, then no reverse and check engine light comes on, and goes back into limp mode.

More than likely you have internal transmission issues. These codes are simply telling you that you have a gear ratio error which is most always internal damage as the input and output RPM is not what it is supposed to be in each gear. The fact that you don't have reverse either is just a compounding of the issue.

If it were me, I would inspect the fluid and make sure it is not low and in good condition and if it not, replace the fluid first.

Here is a guide that will help with this:

https://www.2carpros.com/articles/how-to-service-an-automatic-transmission

Below is the process from the manual for this code. The P0700 code is just telling you that you have a transmission code so we need to focus on the testing for the P0731 code.

Please run through this material and let us know if you have questions. Thanks