Accelerator acting up in GT Sport on PS5

To start with, I only play Gran Turismo Sport. I don't have any other games.

After extended sessions of racing, the accelerator pedal starts acting up. 

One of three things will happen:

1. I cannot get 0% acceleration when letting off. The pedal registers around 1-5% throttle even if I don't touch the pedal.

2. I cannot get 100% acceleration without putting my full weight on the pedal and getting the extra 1-5% acceleration by crushing the rubber acceleration pedal stopper.

3. Maximum acceleration suddenly becomes less than 50% reported in the game.

Please watch this video for examples of all 3 things happening: https://youtu.be/7ZXhhn5_Wdg

Explanations are in Icelandic but I have added English subtitles, please make sure CC is enabled.

So far, what I have done has lead me to believe the fault is not actually in the pedals.

What I have done to try to remedy this issue:

1. At first, I replaced the potentiometer in the accelerator with one that I took out of my brake pedal that broke a few months before, just to see if the problem would change. Was not expecting that to fix it. That resulted in no change, but this did happen more frequently instead.

2. Got a new, unused potentiometer out of a clutch pedal that a friend got with his load cell kit and was not using. Still had symptom 1 and 2 happen but not symptom 3.

3. Got a new entirely untouched accelerator pedal from that same friend, that also had an unused standard pedal assembly. No change, symptoms 1 and 2 still happen but 3 so far has not.

4. Connected the wheel to my PC with updated Fanalab software. Checked for firmware updates, none are available.

Do you have any ideas on what I can do next to try and get rid of this issue?

All help appreciated. 

Regards, Daniel.