An led bulb does not have a connection to ground. The filament in an incandescent bulb draws the circuit back to ground. Essentially turning the circuit off. There is a resistor in the brake switch that connects this. When you mash the brake, power takes the path of least resistance and powers all the lights.
If these trucks did not have a bcm and you changed all the lights to led, it would kill the battery over a period of time.
The front and back turn bulbs are not connected electrically in the switch only through the flasher. Thus when a bulb is out in the back they blink fast, when one is out in the front they just stay on.
Just because a set of led tails has a resistor built in does not mean they will prevent cruise inop. Some are to save the bulbs from a direct 12 volt hit. This also means that they might not have a resistor for the turn signals, which the flasher needs to run correctly. If the truck has 2 brake switches and most all vehicles do all you would need to do is run a jumper wire from the switched side of both switches. That would fix the brake lights and cruise unless the third brake is also led. But for the blinkers you need to wire in a resistor, or an incandescent bulb for each side. Or a dedicated flasher for led turns.