I have had 4 duramaxes,a 02,04,06 and now a 08,my 02 gelled up when it was -2 ONCE,started just fine,ran 15 miles THEN would only idle. I towed it into work that day and had to put a salamander on the fuel tank for 5 hours before it would do anything more than idle. I had filled it at a high volume truck stop the night before at midnight and I went there and filled a 1 gallon container that morning. I let that container sit out in the cold down to -10 and the stuff still looked like gasoline so I never figured it out,the same truck ran fine down to -15 and never acted up again,if I was far from home and it was going to go below -10 I would add some diesel flo to the fuel as insurance. Fast forward to recently,for the first time since then I had a similar thing happen to my 08,I left it sit out overnight and it got down to -18,wasn't plugged in and I didn't have the winter cover on. Started it with no problem with my remote start,let it high idle for 10 minutes,got in it and left for work,the temp gauge was at 200 plus on the motor. I got 5 miles down the road and it lost power and would only go just over a high idle without bogging. Limped it back home and jumped in my van and went to work,that night I put a 1/2 a quart of power service in it and let it idle for 15 minutes at -5. Got in it the next day it was -12 and it drove just fine and has since then,no additive,no cover,not plugged in,nothing. A buddy of mine has a power stroke,a 03 or 04,I called him the day mine gelled up and asked him how his was running,he said he didn't even bother trying to start it when it was that cold from past experience. I never bother plugging mine in since it won't keep the fuel from gelling anyways and starts just fine but it sure does pizz you off to get a few miles down the road abnd have one drop to a idle a barely run. I NOW keep some diesel flo and power service in the truck in case it does it again but I don't put it in since it usually doesn't get much more than -5 around here,Smitty