over the weekend I installed the G56-OFEK that's been sitting on my toolbox for over a month. can't believe I got the transmission back in with a floor jack. I never want to see another floor creeper again as long as I live. anyways the new clutch works beautifully, no more vibration at idle, but there is still a little driveline slack. not nearly as much as with the stock DMF but enough to initially make me wonder if I screwed something up during the install. I did some reading here and on Cumminsforum and everything I've read says this is normal. I've been driving around town and using the clutch every possible chance to facilitate break in. I just need some reassurance before I leave on a 550 mile trip pulling an 8000lb trailer.

 

I've got the same clutch. The engagement/disengagement is more positive than the stocker and that maybe what you're feeling. Mine's fine in forward,but reverse can be a bit grabby once I'm rolling.
Installer insists he left no contaminents on the contact surfaces,so it may be the nature of the beast.

 

As mentioned you are likely just noticing the driveline slack that's always been there but was masked by the sloppy original DMF clutch.

Of course you should get under the truck and check all the U-joints, the slip joints and any play in the rear axle assembly.