I have used stanadyne in alaska for 5 winters with no gell-ups. PowerService (thats diesel kleen ryt...been so long since i looked at a bottle) was my second choice when i couldnt get stanadyne. I have also used one of the additives from napa...i cant remember the name, but it was in a clear bottle and said recommended 4 cummins on it.
There is also this product that you can use if you find yourself with a frozen fuel filter or fuel. Pour this in and it will melt the wax crystals that formed causing the gel. The other product mentioned by chevy*tough is great as preventative maintenance; however, if you are already gelled up this is the product to use.