Double tap T/H??
1st tap of button tuns T/H Mode ON
Push button again.....turns T/H OFF and OD off (no 4th gear)
Push button again..back to normal (default mode)....OD On (1, 2, 3, 4)
Exhaust Brakes......great tool for descending down grades especially when using T/H Mode
I have been running a simple Exhaust Brake System since 2008 on my 2007 5.9 CTD/48RE tranny
Electric Solenoid closes 4" butterfly creating back pressure (2" bypass butterfly controls back pressure).......turn it off and large springs open the 4" butterfly allowing full exhaust flow.
Simple..no air compressor/vacuum pump required
US Gear Decelerator.
(some reports of issues with bushing galling but in 10 yrs have not had any problems.....and I use it a LOT)