ryank1

It is a bad door speaker. Very common for those years. All of the chimes and turn signal noise plays through the drivers door speaker.

Dex 6 is backwards compatible with Dex 3, but you can't use Dex 3 in a Dex 6 application per GM. So to answer your question, you can use either one and per GM you can mix them for you application.

It is a cab mount. https://www.ebay.com/itm/153916113109?hash=item23d61d80d5:g:KJoAAOSwgPVchtrK

Most likely the transfer case encoder motor on the side of the case.

Just one

You need a scan tool that shows individual wheel speed . You will find that one of them is dropping to 0 before the others. This is a sign of either a bad hub bearing or tone ring for the wheel speed sensor. Either way the fix is usually to replace the hub bearing that is dropping to 0 1st.

Between the 2 doors you will have everything you need. On some models depending on options you made need to swap the door harnesses.

The cable is a different length and will need to be swapped, there is also a metal bracket that is different that will need to be swapped.

PDU

They do fit.

The sensors for the 2004 are different than the 2018 and will not work with your truck

Sounds like a bad turn signal switch. The brake lights run through it, but not the 3rd brake light.

Looks like Vent hoses. Most likely one for the trans and one for the front diff. Both should have a cap.

Sounds more like a differential coming apart or maybe in the transfer case. But it shouldn't make a noise when not moving.

What was involved in adding the fog lights?