I just did this exact same thing to my 1356, they slip yoke would start sliding in nice and snug, then got very loose, it showed more when the extension housing was off, I had to replace the extension housing as it was cracked at the bottom, and got a used one from the wreckers, it was the exact same issues, and as leeland's yoke was, mine you could see ripples and necking on the yoke its self. I got a new slip yoke from a local driveline place for 70 ish bucks and ordered the 1356 rebuild kit from bronco graveyard and the kit came with the new bushing. The guy at the local driveline shop warned me that the aftermarket bushings were usually too tight and the yoke wouldn't fit, the one I got was a perfect fit. As for replacing the bushing, the old one almost fell out with a bit more then hand pressure, but I used an aluminum bearing driver to put the new one in and it was tight. To check the bushing, see how wide the oil groove is, you may not need to change it, though if most of its gone(small groove) then it defiantly needs to be changed.
I do also recommend while your at it, to do the oil pump mod so it doesn't chew threw the case and take out your t-case and the washer behind the shift leaver to get rid of the possibility of the shift forks falling off(mine were only contacting it 1/4 of the full engagement.(Do a search, these are very common issues and very easy to fix to make it bullet proof)