From what I have read here and in Diesel Power Magazine, the 7.3 did not meet the EPA requirements, and it was a 2 valve push rod engine. So International developed a smaller, more powerfull 6.0 with 4 valves. It was smaller than the 7.3 , supposed to get better MPG and was going to be the silver bullet for Dodge and Chebbie. Though, it is a very good engine, it had some issues when it first came out. I have a 4-28-04 engine biuld with zero problems, only a two recalls in which I received excellent service for. So not all the 6.0's have issues. There are a lot of posters and trollers who love to stir the pot and would have you belive otherwise.

The Cummins 6.7 is nothing more than a bored out 5.9 with lots of smog stuff. The larger bore is to make up for the lost power with all the additional smog devices. The same is true for the 6.0 PSD, more smog devices takes away power so International bored the 6.0 to 6.4 and added another turbo. I'm not sure what GM has in store for the Duramax. It's my understanding that the 6.6 Duramax will meet the EPA for 2007 with additional smog devices, not sure on the power output though. This years Duramax is the most powerfull out there. It's nothing more than a tuned Duramax with more aggresive tuning profile. It's also my understanding that the programmers for this new Duramax do not provide much more power over stock, since the fuel mapping and timing are allready programmed very high. All this Diesel power wars are being compared to the end of the muscle car era in 1972. that was the year of lower octane fuel, smog pumps, pollution control valves etc.