I will admit it I am a CTW (Certified Technical Wennie) but I thought I would add my ruminations about the new Duramax vs. PSD. I studied the issue some and along with some fellow CTW's we have concluded:
It makes little sense to have aluminum (AL) heads given that: AL expands at a different rate then iron (techincally speaking they have different coefficients of thermal expansion) maybe that is why they have that special head gasket, a sandwitch of ceramic material and tradiditional material. The heads are under a lot of stress both mechcanical and thermal and AL has a elastic limit based upon the number of times it expands and contracts. Iron does not such a limit. Maybe that is why GM says the design life is 200,000 miles while Navistar says the PSD has a design life of 300,000 miles. There is no way to get around the elastic limit problem by adding metal or increasing the number of bolts.
What kind of heads do the big trucks have? Cast Iron

It is interesting to note that GM says the AL heads reduce weight and provide for increased cooloing. Guys this is a HD truck why be concerned about an additional 49 lbs and diesels like it hot.

Early tests say that the Duramax walks away from the PSD pulling a load. OK but lets run that test at 150,000 miles on the engine.
Finally (know everyone is glad to hear that word) GM claims that they tested the Duramax extensively (1,000,000 miles) prior to production. How many road miles are on the PSDs? New and improved is nice but it usually is the enemy of good enough.

It is interesting that GM chose Isuzu over other world class deisel producers like Cummins, CAT, Volvo, Benz, Mack. Or could it be they chose Isuzu because they own 40% of the stock!!