SnoDogs - looks like you're not finding the feedback you wanted and I don't have the 300 either, but maybe I can shed a little light.
The reason you're not getting feedback is that there doesn't seem to be many Cummins powered 36Gs out there. From reading this forum for several years, I've noticed there are a lot of 34Hs with the Cummins and 5 speed that the owners are very happy with. They both (34 & 36) have 2 slides and options for the big fridge and washer/dryer so I would guess there's not a big difference in weight when equally equipped.
In the past the transmission in that package limited the GCWR to 28000#. Since the GVWR was 27910#, the weight of anything you wanted to tow had to be taken out of your GVWR. The new units have a different transmission, still a 5 speed, but rated for 33000# - so that's not a problem anymore.
I like the Cummins engine. From being around it in campgrounds, it seems much quieter than my Cat (from outside, inside I barely hear the Cat).
You might try clicking on the "Find" button just above your post and enter "Cummins 300" (the correct spelling) and also try "Cummings 300" cause you're not the first to misspell it.
There have been several discussions of this package in the past.
Lastly, if at all possible, try to drive both versions. If you're into drag racing motorhomes, the Cat C7 is probably best, but you probably will find the Cummins package more than adequate.
Good luck and let us know how it goes!