03 silverado lq4

I have a 2003 Silverado 2500hd that came with the 6.0/4l80e. I belt the engine and was planning a duramax swap so I sold the original transmission and transfer case. Then I changed my mind and decided to put another 6.0 in it, I found an engine trans and transfer case out of an 01 but the donor truck had the auto 4x4 button where as my 03 had the push button without the auto option, so my question is what do I need to do to make the transfer case work with the truck?

Here’s the problem, my brake lights in the bed aren’t working, but my third brake light and all other lights work as they should. I’ve narrowed the problem down to the VEH STOP fuse in the dash. But that’s where I’m stumped. I replaced the fuse and brake lights work until I put the truck in gear then the fuse blows. Multifunction switch and brake light switch have both been replaced.