New f350 with the exhaust brake button

Tow haul raises the shift speeds. Engine brake on Ford closes the vanes on the turbo to cause back pressure. Ford does not have a valve in the exhaust line as some have had in the past. On my 2012 F-350 both features work at the same time when the tow haul button on the end of the shift is pushed. Separating it into two buttons was a VERY common suggestion, so Ford did it. The change in the 2015 turbo makes exhaust braking through vane control more effective in addition to supplying more air to compete better in mountain climbing contests. Some folks like the higher shift points without engine brake—with two buttons, now you can choose which one or both functions that you want to activate. If the engine brake button is on, the computer will decide when it thinks you want more brake effect and close the vanes. On the 2012, the computer will down shift and close vanes in an attempt to hold speed on a steep decent.