S-10 2004 CHEVY TRUCK 4X4 WON'T DISENGAGE FROM 4HI TO 2WD WHAT CAN CAUSE THIS?

There is a 4wd shift actuator under the truck almost beneath the driver's seat.Mounted to the transfer box. It may have a loose or damaged air hose to it(common on these trucks) Or the actuator needs replacement.You can look up the 4wd actuator for your vehicle on parts store websites and that will help you locate it and troubleshoot it.