When I unlock the tail gate (is it supposed work with the keyless entry?) with the key it unlocks fine. Then, I try opening it again and I have to unlock to have it work.

Is this normal?

 

Yes it is supposed to luck/unlcok with the remote.
The mechanisim inside the door can get jacked up, there are threads on the forum as how to fix it.
Do a search for them.
If I remember right there is a spring that holds the lock up.
That spring breaks or gets weak and it wont work any more.

 

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