Took a ride in a friends new Road Warrior (C5500) this weekend. He has a switch on the dash that downshifts the tranny when you let off the gas. Awesome for pulling my fiver. Do any of you know a way I can add this switch to my 35hundy Alison? Maybe a way to tap into the stock wireing harness and add the dash switch?

Mine only works when you apply the breaks for just the right amount of time and most of the time it's intermitent. Sometimes it down shifts too early and sometimes I just can't get it to downshift on the severe decent till it's just too late and then i'm fighting 4K rpm.

Your thoughts on this would be greatly appreciated.

The switch is for the exhaust brake, when the switch is on and cruise control is off, when you lift off the go pedal, a valve in the exhaust system closes and the trans down shifts. The valve is closed with air. And yes you can add a exhaust brake to any diesel. Is your truck a diesel?

Where is a the switch located. There is a switch near the gear shift lever. This switch will take trans out of OD.
There is another switch that is on right side of IP. This is the exhaust brake. All models before 2006 had a inline exhaust brake. Later models use the Vanes in Turbo for exhaust brake.
On my 2004.5 Kodiak The switch next to gear shift will take trans out of OD even if cruise control is on or accelerator pedal is being pushed.
Exhaust brake and OD operation has changed over the different years of the Dmax/Allison options.
If your pickup can be modified will probably depend on the ECM and TCM. Check out the UP FITTER (http://www.gmupfitter.com/index.html) electrical publications for both Kodiak and Pickup wiring.

AH! exhaust brake. i should have known. Not just the downshifting. I guess the only thing I can do is take it out of OD and rely on my foot braking to get the Alli to downshift. Would love an exhaust brake, maybe in my future, but then so is a C4500.