I'm having some problems electrical in my 04 ram quad cab 4.7 4x4 85k miles

Problem is I have the dreaded fuse #51 that is killing my battery every 3 days.
So I added a relay to out circuit the fuse when I shut truck off and in circuit when I start truck. Something is drawing power and I'm sure its my cluster but this is another story.

My over head temperature display is stuck on -40 degrees and I did some checks and got 1 side of plug going to ground and the other side 5volts.
If i short the connector my display will read 131 degrees so the wires have continuity to the display.

My question is looks like both of these problems are controlled by the FCM front control module.
part #56051036AD and the pcm power control module part #56051039AD.

Would I have to get the same part # for the fcm replacement looking for a used as new is way too much. I know some are different and was wondering if another part# would work.
Same goes for the PCM fuse box. I was thinking if this is bad and not fcm then I would also need a pcm replacement.
Been looking on ebay and can't seem to find the correct part # for replacement.
I did get the part #s off my truck actually looked on the PCM sticker.

So if someone could answer these questions so I don't get the wrong part.

I'm going to remove the fuse box next week and check it out.
I did replace the Temperature sensor today and still stuck on -40 degrees.

thanks for any help