Im a diesel newbie and this is my first winter.

Can someone tell me at what temperture do I need to be concerned with jelling and is there any fuel additive brand recommended for a Duramax? Also at what temp is it nessesary to start using the block heater?

Welcome dad311,
If you do a search for "additives" and "block heaters" and related words you will find a lot of reading to do.
Short version GM Recomends only 2 additives, Stanadyne and Racor
Block heater depends on how cold over night, Personally if it get's below 20 deg f I'll plug it in, and that's into a timer which kick's on about 3 hour's before I leave. If it's really cold and windy I'll have it on for a little longer.
As far as gelling it depends if your local fuel suppliers treat the fuel for winter condition's but most people here use 1 type of winter additive or another and have been running at -20 deg f with no problem's.

If your a newbie to diesel spend some time here and read up on all the past pages of post's and you'll learn a lot. And don't forget to read your owner's manual and the diesel supplement so info there too.

Good Luck

Diesel Dragon

Just start putting in a fuel additive (such as "Power Service" from WAl-Mart or auto stores) and you won't need to worry about Gelling. You should start using the additive on all your fill ups. There is plenty of info on this site about them.

You don't need to use your block heater until way below freezing. but check your manual. There is info on this on this site also.

Diesel fuel will not pour at around 10 degrees, according to one of my mechanics. You shoudl always use an additive, just to keep water from getting to your injectors. You can research this throughout this site. The best additive I have seen and is recommended by GM is Stanadyne. If you should happen to get some gelling, you can acquire some rescue 911 from one of the truck stops or automotive store.