Bart- as I prepare for a similiar project sometime down the road. I looked into the cruise control requirements.
There are a lot of conditions that need to met. I began studying the wireing diagram for an escalade. I never came to a conclusion but did realize it was not simple, it can certainly be done. This guy does it all time,
http://hccperformance.com/index.html , I contacted him. He told me it took them so long to figure it out he would not release the info.
For whatever it's worth.