2006 GMC Envoy: I tested all of the fuses and all of them check out but my power locks, cabin lighting, dash panel lights, etc. aren't working.

Which fuse box ? Do you know what a DDM -is ? Driver door module . Do you have any idea what all is involved in making these thing's you have listed work ? A lot more then a fuse , there could be DTC'S - diagnostic trouble codes stored in the principal Control module ,the BCM , That could save a tech. valubale time in diagnoising this problem !
Door Lock System Components
The power door lock system consists of the following components:
• Driver Door Module (DDM)
• Passenger Door Module (PDM)
• Liftgate Module (LGM)
• Door lock relay
• Door unlock relay
• Body Control Module (BCM)
• Reversible door lock actuators in each of the doors
• LR/RR LOCKS 10A fuse (relay supply voltage)
• Door lock switches in driver and passenger doors (switches are integral components to the DDM and PDM)
Did you know there is a fuse box in the rear of the vehicle ?
Fuse Block - Rear
Beneath the left rear seat
The inside lights are also controlled by the BCM , and the fuse's are also located in the rear fuse box .
The body control module (BCM) directly sends a 5-volt reference voltage to the instrument panel (I/P) dimmer switch which is then adjusted based on the I/P dimmer switch position and returned as a low reference and a signal to the BCM. The BCM uses this signal to directly control the desired level of instrument panel illumination lamp intensity.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC B2620 Display Dimming Pulse Width Modulation (PWM) Input Circuit. There are several DTC'S that can set !
DTC B3801 Passenger Compartment Lamp Request Circuit
DTC B2610 Passenger Compartment Dimming 1 Circuit plus others for power locks .
Thank You Uncle Sam