I have a 98 Jimmy with the 3 buttons on the dash. Everything started last winter when I tried the 4x4. I was at the mall (in 4x4), backed up from the stall, put it in drive and did not have any wheels engagement. The engine was reving, but was not going anywhere. Played with the transmission shifter and got it going again. After that time I tried to use the 4HI and It would not go to 4HI, the light would blink and the 2HI light would come on. No switch appened. I was able to go to 4LO. I replaced the Motor/Encoder and everything seemed to be working without the engine running. Took it for a spin and the 4HI engaged once. I stopped, put it in neutral tried to switch it back to 2HI and nothing happened. Again the engine was reving without any engagement. I switch it to 4LO in emergency mode. Then I was able to switch it back to 2HI. I checked the vaccuum hoses and they seemed good. Checked the vaccuum switch, and the ball inside was stuck. I replaced it, and the 4HI worked again (without driving the truck). Took it for a spin. I was driving in 4x4, stopped at a red light, while waiting I switch it back to 2HI and nothing happened. The red light turned green, tried to go but the truck was not going anywhere. I had to switch it to 4LO the emergency way. Then I was able to switch it to 2HI. Never able to switch in 4HI. The light would blink, and would go back to 2HI. After playing with all 3 switches trying to get the 4HI going, I loss the 4LO too. Now nothing happened in 4HI and 4LO. I can hear the TCCM relays switching, but cannot hear the motor/encoder moving anymore (used to). Is it another motor/encoder that I have to replace? If yes, why did it stopped working after a few hours? Did it burned out? Any help would be appreciated.