Whoo Hoo!!! Check Engine Light Just Came On

[Hummertech]

If you leave your gas cap loose, the reason it can take a few days for the light to come on is this. The computer looks for 2 consecutive failures before it will turn the light on. It doesn't always run the test every time you drive also, it has to have certain criteria met before it can run the test (temp, speed, etc..).
That is why it often take a day or two.
As far as the problem with no power. If your truck ever does that, shut the truck off, wait about 10 seconds and start it back up. It will probably be fine then. Sometimes the Pcm and the elctronic throttle motor will lose communication for a millisecond, and then go into that default mode. Some trucks can have a updated calibration programmed into them to help prevent this miscommunication.
Hope that clears this up.
Let us know what your dealer does, or doesn't do.