You needn't close the tailgate to check if the unlatch motor is operational.
Open the tailgate and trigger the latch closed with a screwdriver. Then see if it unlatches with either the fob or unlock button.
This will exclude any issues related to misalignment.
If it still doesn't unlatch, then it would be down to
1. Unlock signal actually confirmed at the lock assembly. You ideally need a wiring diagram and a multimeter for this.
2. Wiring integrity as gregers says.
3. The lock/latch motor itself. There is a TSB out on this, so it isn't an isolated issue as one might assume.