Q: Truck will not start or crank with the key bit all lights are on, 2008 6.6L gmc 2500

It sounds like what you are describing may be related to a faulty starter relay or some faulty wiring that may not be producing a proper connection to the starter. The starter relay directs power from the battery to the starter solenoid which then engages the starter when you turn the key. When this is not working properly, you may notice intermittent starting problems including no response when turning the key to start. Generally, when this does fail, it does so very randomly and usually without warning other than intermittent starting. The power from the battery will still power other accessories such as radio, horn, etc., but you may not have any power to the starter. I would recommend having an expert from YourMechanic come to your location to diagnose and inspect your vehicle.