The transition shift arm on your steering column gets worn out with age. There's 3 arms. Centre one has a small nub on both sides. The nubs get worn and won't slide smoothly into the other shift arms.
You can get lucky and just pull the arms back to nuetral position or use a big screwdriver to help pop them back.
In some cases you need to get under the truck and tap the arms on the tranny back to nuetral. Make sure your truck can't roll away though. When you get it back to normal the best way to shift from 1-2 is to shift up towards reverse and then down slightly and over and up to 2nd. Takes a little practice but still carry a big screwdriver in the glove box in case you need it. LOL!!!