Rear turn signals and brake lights out. Front signals and rear tail lights work fine.

Stop Lamps
The brake pedal position sensor is used to sense the action of the driver application of the brake pedal. The body control module (BCM) provides a 5-volt reference voltage and low reference to the brake pedal position sensor. The position sensor provides an analog voltage signal back to the BCM that will increase as the brake pedal is applied. When the brake is applied, the BCM will then apply battery voltage to the left and right stop/turn signal lamp supply voltage circuits and the center high mounted stop lamp (CHMSL) supply voltage circuit illuminating the stop lamps. At the same time the BCM applies battery voltage through the signal circuit to the transmission control module (TCM) and the engine control module (ECM) indicating that the brakes are applied.
Ground for the stop lamps is supplied as follows:
• G402 provides ground for the left rear stop/tail/turn signal lamps
• G403 provides ground for the right rear stop/tail/turn signal lamps
• G301 provides ground for the CHMSL
The stop lamps on this vehicle will not illuminate unless the ignition is in the accessory, run, or crank positions. When the ignition is in the OFF position the stop lamps will not illuminate when the brake pedal is applied.
Battery voltage from the LT TRN/SIG and RT TRN/SIG fuses located in the rear fuse block is also used by the body control module (BCM) for stop lamp operation.

Turn Signal Lamps
Battery voltage supplied to the body control module (BCM) from the fuses listed below is used for turn signal and hazard lamp operation.
• LT TRN/SIG fuse for the left turn signals
• CTSY/RF TRN fuse for the right front turn signal
• RR TRN/SIG fuse for the right rear turn signal
When the turn signal switch is place in either the LEFT or RIGHT position, ground from G300 is applied through the turn signal switch signal circuit to the BCM indicating the turn signal request. In response to this signal, the BCM applies a pulsating voltage to the front and rear turn signal lamps supply voltage circuits cycling the lamps ON and OFF. At the same time the BCM sends a GMLAN serial data message to the instrument panel cluster (IPC) to cycle the appropriate turn signal indicator ON and OFF.
Ground for the turn signal lamps is supplied as follows:
• G104 provides ground for the left and right front turn signal lamps
• G402 provides ground for the left rear stop/tail/turn signal lamps
• G403 provides ground for the right rear stop/tail/turn signal lamps

Do you have a factory scan tool (tech2) ? Your best bet , take it to the dealer .

it all points to a fault with a common ground. Find earthing points

bad lamp is my guess,

Sounds like you lost the ground to the rear lights.

check the relays and connections at the tail lights and under the truck, has the truck ever been off road or in deep water?

Your turn signal lights and brake lights are the same lights . Question : do the front parking lights work ? The front and rear running lights or parking lights are all on the same circuit and fuse . If the front lights work , and the rear lights don't , make sure the bulbs are good first . If OK , I would suspect the problem is either a bad ground in the rear taillight wiring harness or a bad connection in the rear taillight connector Itself .

I'm inclined to believe it is the turn signal switch. When you select left or right, the brake light is removed from that side, and the flasher is connected to the bulb instead, making the brake light on that side flash as the indication that you plan to turn. You have lost everything, but the simple answers check out.

If you have lost signals, brake lights and tail lights, then it is more likely that the ground supplied to the bulbs is not working, since the tail lights share noting in common with the brakes lights and turn signals but ground.

If the tail lights work, the fact that the brake lights and rear turn signals share that switch starts to look meaningful — even more so if the front turn signals also don't work. But the front signals and the rear signals use different circuitry in the switch, so it would be something more mechanical in the switch than electrical in that case.

Bad earth connection.Clean or replce wire.

I have taken my car to many shops to solve this problem. Long story short your tail light has a bad circut and entire lamp must be replaced. (Lamp cost approximate $130.00)

TURN SIGNALS WILL FEED BACK THROUGH THE TURN SIGNAL SWITCH.THEY ARE INDEPENDENT OUT SIDE ON THE CAR BUT NOT IN THE SIGNAL SWITCH.REPLACE THE SIGNAL SWITCH