my 2005 2500hd shutters and grabs weird (sort of clunks also) during left turns only when it was -10F today. It reminded me of turning a corner in a race car with a full posi-trac rear end. It sorta feels like it is trying to push the front straight and is fighting the turn. What might be causing this? I had it out of 4WD if that matters....

35,000 miles on it with no mods other than bulldog

The limited slip sometimes gets sticky if you don't ever spin your tires. Yours probably has something to do with temp and your gear oil being pretty thick. Try spinning out to break the limited slip loose. You might want to drive a little ways to get the oil loosened up a bit.

There is also a friction modifier that you can add to the rear end to make things a little better on your limeted slip. Not sure who all makes it.

Well your intentions are good JRS but this isn't a clutched limited slip rear end like a 'posi' unit. The G80 requires no friction modifiers it's a mechanical type locker.

I have a locker rear in my 32 Ford, it such a small light car, it would just jerk around corners, Amzoil sells a rear end additive, put that in and rear is smooth and quiet. Check with one of the Amzoil vendors on DP, see if they can help.

This is what I added, again check with Amzoil rep to see what they think, best money I ever spent.

https://www.amsoil.com/storefront/ada.aspx

I remember fords limited slip using a small bottle of motocraft friction modifier. That was what I was going by. Serves me right for trying to do anything right with ford knowledge;)