I have a 2014 Ram 1500, and am having similar issues with my cruise.
It started off as randomly not turning on with the steering wheel button. Holding the gear +/- buttons wouldn't help, nor would smacking the steering wheel.
Now it has progressed further. I can turn cruise on right after start up, and even use it if I am fast enough. But after a few minutes, a quick message on the instrument cluster says "Cruise control off" and then it will not turn back on. If I engage cruise within a very short time, it seems to stay active until it is deactivated for any reason. Then in short order I get the "Cruise Control Off" message and it's out of order.
I have a code reader that can go into all the systems, but what am I looking for?
Any other troubleshooting ideas?