I went through last winter in northern New England without a problem
with my 2003 Duramax. Without plugging in the block heater, I had no
problem starting as low as -10F in the morning. I would recommend
that in that kind of weather, you should make sure your batteries are
in good shape and use synthetic 5w-40 oil (which can be used year
Of course, all bets are off if your fuel is not winterized.
One thing about the Duramax is that it warms up slowly. In winter,
even with a 10 mile one way commute, it may never fully warm up.
However, GM supplies with the truck a grille cover for winter use if
you feel you need to build heat faster.
Ray 2500HD GMC SLT Crew Cab 2003