I have a 2000 Chevy Silverado 1500 4x4 with an 5.3 liter motor and auto transmission. Over the past few months the truck has failed to go into 4 low at times and the service 4 wheel drive light comes on once in a while. I changed the transmission and transercase fluid but the light continues to come on sometimes. Now it will not engage in either 4 low or 4 hi. I have a push button selection on my dash to engage the 4 wheel drive and neither the 4 hi or 4 low will light up or engage. If anyone has any ideas of what could be going wrong, please let me know. Thanks!