My 2001 chevy blazer is stuck in 4x4 low range. I have replaced the 4x4 selecter switch and it still has this problem. I cant figure out if its the actuator on my transfer case or a bad vacuum line or bad vacuum actuator or that my 4x4 relay under the dash is bad or it might be none of the above. When i push the 4x4 high or 4x2 high or automatic 4x4 button the button will flash i will hear the relay under my dash click and here my front end make the shifting noise. This will happen 2 or 3 times then it will say its still in 4x4 low range. What could be causing this?