then I very much still don’t understand why the truck acted like it was in neutral

 

It's all about pressures. The PCM controls it, so, if it is getting bad information somewhere, or, the solenoid is not behaving properly, odd things happen. Unplugging the 8 pin connector takes the electronics out of the equation. If the trans work in 'manual mode', then the problem is most certainly in the electronics.

 

It’s just such a bizarre issue to have, especially considering it works perfectly normally

 

That's the fun part of just about any electrically controlled do-hickey.

 

I rebuilt the 46re transmission and didn't see the wire to crankshaft position sensor and smashed it but replaced sensor and I took pictures of the eight pin plug before removing and even starting to remove it but I wire by wire after hunting for pin layout and wiring diagram together and hope it's correct after all of my attempts at saving the plug connector because wire by wire I backed out of plug and heat shrank the wires because they where bear like two inches and im sure helped burn up the trans but it was bad and it plugs in and don't hear any click on selonoid or anything from trans unless I jump relays and all it will do is turn over no spark