4WD lights are both flashing and it is not working in 4Hi

2003 chevy blazer, 4hi and 4lo lights both flash and go back to 2hi. Only in neutral do I get a response from the switch in drive it does nothing. It will go into 4lo just fine. Checked the tccm for bad connection and corroded wires cleaned reassembled and unooked the battery to reset the tccm and still nothing? No visible vacum leaks, actuator under the battery has no leaks, I did notice with the vehicle running there is no vacum coming out or going in from the vacum line that goes to the actuator under the battery. Im at a loss! There is no vacum switch on the firewall like some other models I have read about. I also changed the 3 switch panel on the dash and still nothing. HELP!