Go into your control panel, and add your car’s specs there, in your signature. It will then show in the bottom of all of the posts you do.
If the problem was with the 12v going to the ECU, or the. ECU ground, then I would think that you would see your issue in more circuits, instead of just one. Again, you say that, when testing the pin AT the ECU, that you get 5v....but then it drops off? It drops off AT the ECU? Perhaps it’s far easier to run an entirely new wire from the TPS to the ECU, in place of the grey/red...????