Help!

I have a 2002 4 door s10 Blazer with 4WD and my rear differential went.
I like to tackle projects, but am still a noob when it comes to the more intricate stuff. Found a used rear assembly, removed my old one, and replaced it with the new. everything lined up properly with the leaf springs and U bolts, and the rear sway bar? I put new rotors on, and the disk brakes on rear were replaced, and everything fit fine with the calipers and all. However, after getting all of that installed, I go to connect the front of the differential to my drive shaft and it is about 2 inches too short! Could there be something I'm missing? Is there any way to get more slack on the drive shaft? Or from the differential side? Hoping they did not give me the wrong rear end, cause that was a lot of work! It's supposed to be the correct rear. My old rear was the 3.42, 7 5/8" GU6 option, and that is supposedly what they gave me. I couldn't find a tag on this rear verifying the option, and was hoping someone might give some input before I go pulling the cover off of the rear to verify.

 

The front of the driveshaft slides into the rear of the transfer case. My guess is you have the yoke slid all the way in, simply slide the driveshaft back far enough to attach it. It has to have movement back and forth to allow for the spring compression and such