Is the DIFF light on? Did you try to push the button and go in reverse or low speed and wait for it to disengage..or try to go down a hill to disengage. Is it difficult to steer? With diff lock on it's tuff to steer vs just the 4WD. I know I have that issue sometimes when it's in 4WD but in motion, it will not disengage. You need to disengage DIFF lock then the 4WD.