It should shift easily thought the different positions when the transmission selector is in the neutral position.
First thing to try is disconnect the transfer case shift cable at the transfer case and see how easy it is to move the transfer 4x4 lever with it disconnected.
If the lever move easily through all the positions, then your problem is in the transfer case, not the shift mechanism.
If you find the problem to be the transfer case itself, you can rebuild it, have it rebuilt, or find a used one in a salvage yard.
They are simple manual boxes and fairly easy to rebuild.
Not a lot of parts in them that wear out.
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Supporting Vendor and Moderator of LOST05 Jeep Liberty CRD Limited
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