CHEVROLET SILVERADO TRANSFER CASE SELECTOR SWITCH

I Just Came Back To The Truck After It Was Sitting For A Year, And The 4-button 4wd Dash Switch Lights Up When The Key Is Turned On But...

For Years My Truck Will Switch From 2wd To 4wh By Itself But Only When I'm Braking (periodically). It Will Not Switch Back Unless I Turn...