Service 4WD Message Light

[dmarty]

I have a 1999 Silverado LT 5.3, auto-4WD with 271k miles. I've searched other threads on this problem and the answer is not clear. The "Sevice 4WD" messeage light comes on every few days. It always comes on in 2WD when driving on the highway at 55 to 65 mph. When I stop, the 4WD seems to work normally (although it's hard to tell on dry pavement in the summer, but there appears to be plenty of driveline windup) and the next time I start the engine and drive it, the mesage light is not on and will stay off for a few days to a week. I have not used 4WD since last winter. I had a similar problem at 112k miles when the dash 4WD auto control failed. At that time, the dash control lights blinked in a goofy way and the 4WD refused to engage when I tried to use it. I replaced the dash control and everything has worked fine until now. Most of the other threads say it's the dash contol unit with one claiming it's either the front axle actuator or the transfer case actuator.

My questions are: Can the dash control fail in different ways or are the symptoms this time indicating a problem with either the front axle or transfer case actuators? Should I keep driving it until it fails completly so it's easier to find the problem? If I do, will it leave me stranded? Will an aftermarket code reader give me a more detailed code explanation or will it have to be connected to a Tech2?

Thanks,

dmarty