This truck is my first auto trans,68RFE,I miss granny gear.
The E-brake is not very useful on back country roads at slower speeds,it cuts off @1200 RPM,a G56 may work a little better,at least that is my impression from reading the posts of others.
There is a road I like to drive,an old stage coach road that has been paved,but it is narrow,in a gas truck I could use engine braking with occasional taps on the service brakes to keep at a safe speed.
The combination of 68 auto,TC unlocking,no E-brake below 1200,3.42 diff. and 315/70/18 tires allow the truck to roll faster than I would like.
Sure,I can use the service brakes ,but,I think if I had a G56 it would purr down this hill in 3rd/E-brake just like my V10 did.
Most of the time the auto is OK,it gets up to speed on a freeway on ramp better than the NV4500 did.
The Cummins is detuned for the manual,but I suspect more power is delivered to the rear wheels through a manual trans VS a slush box.
I would like to see dyno numbers comparing the two.
There doesn't seem to be a perfect trans,you have to give something up with either one.