Default Problems Unpacking/Packing kernel

Hi!

I am trying to create a custom kernel for my Galaxy Note 3. I have successfully modified and built the kernel. Now I want to actually test it. I've searched for possible methods to create a boot.img file from my zImage. I've tried
  • mkbootimg and unmkbootimg
  • kernel kitchen

I was able to create a boot.img with both methods and both of them failed to boot. I thought I messed up the kernel, BUT then I tried to just unpack a stock boot.img and repack it again - and this also failed with both methods.

Seeing as there are already people who made custom kernels for the Note 3, I'm wondering what I am doing wrong. Also I'm a bit new to this, that may also be a factor. Could someone possibly give a hint what might be going awry? Will of course provide additional information, if required.

Edit: nevermind that, found out I need Snapdragon 800 patched mkbootimg tools. found binary versions of them on github (Can't post link because I'm a new user). unsure where the source code is though.