I have a 2000 Gmc Sierra, that won't shift into 4wheel drive , the shift lights blink and don't shift ... Is it possible that the 4wheel drive actuator is bad and needs replaceing ?? If so is this something that I can do in the driveway with jackstands ???? PLEASE HELP ...

 

Yep, could be either one, the tcase actuator, or the front diff actuator. Have a buddy push the button, if the tcase one works, you can hear it if you put your head under the truck, probably hear it if you just open the door without the truck running and push it. You can do either one in the driveway without too much trouble. Front one is a little easier. Good luck, I had both go bad within a month of each other.