Took my 2011 cargo 5.3 on it's first long trip and figured out the factory cruise control only works intermittently. The on off switch lights up on the steering wheel but hitting "set" button only activates it once in a while. It works great until it has to be cancelled and won't activate again. It may come on again later or it may not. For the most part it won't.

My first thought is the switch but wanted to see if there are common issues before I dig into it.

 

Looks like I figured it out. Turned out to be the brake light switch. It has two outputs on each side of the rocker switch. One goes to the computer while the other goes to the brake light circuit. The switch was worn to the point where it was keeping contact with the output going to the computer so the cruise control system thought the brake was applied.

In the picture below the new switch is on the right. You can see the left hand contacts are wide open. On the old switch one is closed and the one below it is almost closed. It looks like the contact that controls the brake lights is naturally farther out and as the switch wears you lose cruise control before it fails to turn off the brake lights.