Tmarqjr

I recently aquired a 2007 chevy silverady 2500hd 6.0 gas and 6l80 trans. Bought it off the company i work at, so it is a used work truck. But has been maintained by me so pretty well taken care of. Has 200k miles. This is a problem that has been here for a while but managment didnt seem it important enough to set time to. Now that its mine i would like it to work. The cruise control isnt working. It has the buttons in the center of steering wheel not the multifunction switch. I can press the on button and the light lights up, but when i hit set for speed nothing. Once in a while i will press set and the green cruise indicator will appear on dash and will actually work for longest i had was 2 seconds then shuts rite back off. I have replaced the brake pedal switch and ohmed it out with pedal pressed and released about 8 inches up wire with a tap, and is functioning correctally. Wich made no difference from old to new brake switch. I have just replaced the buttons in steering wheel and that to has made no difference. Checked the fuse under hood and cleaned and replaced no difference. I put the scanner on it ( solus legend from snapon) and went to the. Cruise controll tab and it has 3 info lines one for the brake swich with activates and deactivates when pressed( as suposed to) and one for the manual shift butons on shifter and those reading correctly when pressed. But then there is the line for cruise controll switch. Wich says off. I watched this page while driving down verry bumpy dirt road and every now and then it would flicker to on. And i would hold set button and i would see set come up on screen. But would not phisically activate on truck. And when back on smooth road always said off. So im thinking bad and/or loose connection, or maybe a computer/module going out. So was woundering anyone know where to start without wanting to take whole harness out and clean and grease everything, what would important connections and control modules be in the operations of the cruise control.

edit: no engine, transmition codes. Tcs amd abs systems are also code free and fully functioning correctly.