Hello and welcome to Just answer.com, Super mechanic here. About your vehicle.
It sounds like it might just be a bad tranfer case position sensor. Let me give you tests for the trouble codes. Notice that on the P0837 it says to address any other tranfer case codes first, (the P0839)
SYMPTOM P0839-4WD MODE SENSOR HIGHWHEN MONITORED Continuously with the ignition key on.SET CONDITION When the 4WD Mode Sensor input circuit voltage raises above 4.78 volts for 5.72 seconds .POSSIBLE CAUSES
SYMPTOM P0837-4WD MUX SWITCH PERFORMANCEWHEN MONITORED Continuously with the ignition on.SET CONDITION The 4WD mixed switch input detected in an invalid range or irrational switch state.POSSIBLE CAUSES