OK I know that a T42 needs an ISS (Input Speed Sensor) to work, but some 4L6xE have ISS but still have the older style Manifold Pressure Switch.
I don't know for sure which TCMs support the newer style valve body and mode/gear selector.

My hunch is that your TCM was designed for the older style Manifold Pressure Switch and we need to go back to that and then debug the problem from there.
These subtle but significant changes by GM have confused plenty of people. And you saying it was a 2013 trans threw everyone here as it seems to be a 2006 trans.

 

I don’t usually disagree with mrvedit but the trans worked fine before these so call technicians started missing with it. I would have them put everything back the way it was, the way that the transmission worked before they got their hands on it. They are going about this all wrong. Vorteciroc is right on the money with what is going on with these parts and what parts work with each other and has explained it very well.

You need to find a wiring schematic for a 2008 Chevy Silverado and then go from there. The way I see it if you want your CC to work you have to options.

Option # 1 install a factory type Automatic Transmission Park Neutral Position Switch Assembly on the outside of the transmission and wire it to your E38 PCM using the correct wiring schematic.



Option # 2 I think that you can use the Dakota Digital GSS-3000 range sensor that you already have. Using the wiring schematic that I posted in post # 16 for a 411 PCM as an example. I think all you would need to do to make the Dakota Digital GSS-3000 range sensor work is to supply a switched ground when in park/neutral from the Dakota Digital GSS-3000 sensor to PCM connector C1 pin 34. I would have to see the instructions from the Dakota Digital GSS-3000 to know for sure if this will work. Also you will need to use the correct wiring schematic to know which connector and pin to wire to on your PCM.

 

One of the solutions my cruise vendor mentioned was in fact putting the park neutral switch on the outside. That would leave the issue of getting the signal for which gear I'm in to the gauges. That can be figured out. Wiring for that switch would be an issue. Not sure... Maybe programming changes from PSI too?

Yes, going back to original internals should be imminent.

 

Sorry mrvedit you posted while I was typing. Yes need to put everything back the way it was and follow my post # 42.

 

Actually, I think what I said was that I purchased it from a Chevy dealer in 2013, and I provided the part number..

It's very obvious to me that the dealer figured I'd never know the difference and they offloaded old inventory. I called and specifically asked for a 4L70 when I ordered it.

 

No need for program changes, the transmission worked before people got their hands in it. The PCM just needs is see a ground when the trans is in park/neutral to one pin. All you need is a switch and can supply that ground and the correct wiring schematic for you PCM to know which PCM pin to use then your CC should work. You are making this way more complicated than it is.

 

Agree with Mr Bond that you need to restore the original internals. Once the trans shifts again, I am confident that a proper scan tool like HP Tuners will prove that the PCM knows which gear the shifter is in. And perhaps the external range switch will also be needed so that the PCM knows if the shifter is in Park or Neutral. Your Dakota module might be looking at both signals (PIDs) to determine when to enable the cruise control function.