Pull the shifter and make sure it is stabbed into the shifter forks properly. If you are in 2H, then make sure to get the end of the shifter into the 2WD/4WD fork, should be the one on the right side. I usually like to shift into 4H before pulling the shifter because then both slots are lined up and it is easier to get things lined up. Even so, I usually miss half the time, so put in a bolt or two and make sure it shifts right before buttoning things all up.