Diesel vs gas......................

As I said, many factors about the drivetrain are considered, for GCWR rating. Longevity of service is one of those factors, and is why the diesel has the higher GCWR rating. It (diesel) can handle the higher load, without wearing out as fast. Yes, the gasser can generate more horepower, and could handle more GCWR load than the diesel, since it has more horsepower. But, the gasser would NOT LAST AS LONG as the diesel, since the gasser would have to turn 5,000 RPMs all day in order to do it.

I believe that the 8.1 produces its max HP at around 4000 rpm, not 5000, but in any event, both the 8.1 and the DMax are rated as 200,000 miles engines. Since they have the same GCVW ratings in all except the 3500 with the Allison, it would seem that GM at least believes that the 8.1 gasser will las just as long as their DMax diesel doing exactly the same amount of work.

But, as many have said, it gets into economics - a big block V8 gasser that could turn 5,000 RPMs all day long and still last 200,000 miles, would be a VERY expensive engine to build, and would cost too much to put in regular production trucks. Much cheaper to just give the gasser a lower GCWR rating and gear it to not turn so many RPMs. Then, offer a diesel engine with a higher GCWR rating, since even though it has less maximum horsepower, it can still generate enough horsepower to move the bigger load, and do it without twisting as hard.

See above. GM says that the 8.1 will do just that and it is quite a bit cheaper than the DMax.

Bert