O3 avalanche z71 transfer case acuator switches from 4 low to 4 high to 2 high by its self

sounds like the transfer case needs rebuilding or replaced check to see if the oil in the case is dark or colored or milkey looking this is a indication the transfer case need to be redone

i would suggest taking to a 4wd repair shop as will need diagnosing with the proper equipment

On those year models with the switch on the dash the switches are bad about going out but the actuator is located at the front passenger side on the transfer case if its a z71 drop.the skid plate on the front and its black about 4 inches long with a short couple of wires coming out the end of it to a plug. Disconnect the battery and then unplug it and take it out a short cressent wrench is best and then just put the new one in but don't over tighten

I don't know what you mean3010 mule is this a chevy . If so look at the acuator cable and the actuator it self and the front carrier switch as well as the shifting mechizium switches for the 4 wheel engage system adjustment and vacuum positvve pressure to the transfer case and transmission

I would check the shifting mechinizuns . If its manual _ cable opperated system have someone shift it see how it moves on the transfer case and how smooth the cable opperation is . The system is bascaly a vacuum opperated system after that but if it goes into 4 wheel then the system is working . The other place you could look is at the front transaxle adjustment _switch witch is a cable opperated system that is controled by a vacuum switch on the transfer case and an acuater under the battery tray to pull the cable with the froce of the vacuum from the transfer switch engine vacuum . If you have an electronic shift control inside the cab it still works basicaly the same way except you have another electrical switch to check. It dosn't sound like you have a big problem because the system works it goes into 4 wheel but you need to find out witch part or switch is sticking mechicaly or if its an electrical switch sending or not sending the correct signial to its compontets

Did you ever think of having it diagnosed by a qualified repair shop ? Thier are aspects associated with this system you have no clue about. That's the first thing every one goes for , changing the switch . It flashes because codes are stored .
DTC B0768 Service Indicator Circuit High
DTC B2725 ATC Mode Switch Circuit Malfunction
DTC C0300 Rear Speed Sensor Malfunction
DTC C0305 Front Speed Sensor Malfunction
DTC C0308 Motor A/B Circuit Low
DTC C0309 Motor A/B Circuit High
DTC C0310 Motor A/B Circuit Open
DTC C0315 Motor Ground Circuit Open
DTC C0323 T-Case Lock Circuit Low
DTC C0324 T-Case Lock Circuit High
DTC C0327 Encoder Circuit Malfunction
DTC C0357 Park Switch Circuit High
DTC C0362 4LO Discrete Output Circuit High
DTC C0367 Front Axle Control Circuit High
DTC C0374 General System Malfunction
DTC C0376 Front/Rear Shaft Speed Mismatch
DTC C0387 Unable to Perform Shift
DTC C0550 ECU Malfunction
DTC C0611 VIN Information Error
You need a professional scan tool to check for these codes an too view data parameters .
Transfer Case Shift Control Module
The transfer case shift control module uses the VIN information for calculations that are required for the different calibrations used based on axle ratio, transmission, tire size, and engine. The system does not know which calibration to use without this information.
The direct battery supply line (CKT 1640) provides the power to the module and motor circuitry.
Transfer Case Encoder Motor
The transfer case encoder motor consists of a permanent magnet (PM) DC motor and gear reduction assembly. It is located on the left hand side (drivers side) of the transfer case. When activated it turns the sector shaft of the transfer case (clockwise or counter clockwise) to shift the transfer case. The encoder motor is controlled with a pulse width modulated (PWM) circuit within the transfer case shift control module. This circuit consists of a driver on both the Motor A and Motor B circuits. The encoder motor is bi-directional to allow the motor to shift the transfer case from 2HI or 4HI to neutral and 4LO positions.
Transfer Case Encoder
Your best bet ,take it to a qualified repair shop .

Have you received any failure codes (check engine light)? If you have, find out what they are by going to any parts store and they can read your failure codes for free. Let me know after that.

Ckeck the acuator motor on the transfer case it may be burned out. With the key on (motor off) transmission in nutral try switching from 2 to 4 wheel drive and back you should hear the acuator moror run folowed by a click each time you activate the switch.

it is most likely your transfer case.if it is your front axle that is having problems .take it in to be checked

possibles--chech and test 4wd / transfer case module --faulty switch --- transfer case failing