I rode in a buddy's 2014 3500 Cummins/68 combo recently and was surprised how poorly his exhaust brake performed compared to the one in my G56 equipped truck. I asked him why he doesn't run in Tow/Haul mode and he said that he can't stand the harsh shifting of the transmission in this mode so he rarely uses the exhaust brake around town.
I use mine all the time in Full mode and love how it works down to just below 1,000 RPM. It works fantastic even creeping around hilly campgrounds in 1st gear with the 16k fiver in tow. :)
In the city, I rarely have to shift out of 5th gear if I watch traffic because the truck will easily lug down to around 15 mph and pull out of it in 5th without touching the brakes. :B