Engine/transmission braking in gas engines

Thanks for all the good information. The trani brakes are a great feature that I would happily use if on my rig. I was starting to use that as a major criteria for buying a coach. But if I can accomplish the same thing manually as I have for several yrs with my pickup towing a TT, I will bump this down to a secondary criteria. I was not sure if the engineers had done some funny business with the gas engine also to help with braking.
Thanks again