Thank to all of you for your input. I'm fairly new at the RV scene and am still learning all of the details about selecting the proper equipment.
The GMC line of trucks is well proven and the Duramax engine , from what I have been able to learn, has an excellent reputation, as well as plenty of pulling power. It also is relatively quite for its power output. Besides, the Allison transmission that comes with the Duramax is as good as they come.
I knew that the Nissan Titan XD was not a true 3/4tn. model like the GM, and that the 5.0 Cummins engine was not as powerful as the Duramax.
I just wondered if the commercials about the Nissan were stretching it about the hauling and pulling capabilities. Good to have folks like you out there who have a good deal more experience with this stuff than I do. I appreciate all of your input.
Now go get on with spec'ing a GMC/Duramax.