97 blazer 4x4 40,000 miles with push button 4hi and 4lo the problem is it will engage in 4hi when needed and back to 2hi after a few times of doing this it wont engage in 4hi. 4lo still works but no 4hi. But if i disconect the battery for a few minutes and reconnect it works again for a while then after a few times of engaging 4hi and back to 2hi its back to the same problem. why does disconecting the battery reset the problem?