its just going to leak everywhere inside if you stuff it. like cool said, find the 2 black hoses that run to it and bypass it.

 

As mentioned you can bypass the hoses from it under the hood but eventualy your going to need heat so why not just replace the heater core and be done with it?

 

At this point I do not have the time to replace it. Once i am able to have a weekend free to tear it apart I will I've done heater cores just not on GMC's before. Can anyone give me a quick run down of where I can find these hoses? pictures, or a how do would be great!

 

Nevermind, I found the two hoses, and tied them together with another hose so they just recirculate. thanks guys!