Tonight I had a few minutes to play with the truck, so I tried to find a couple of small things to mess with. I noticed a pin sliding out of the gear shift lever. As it was the pin holding it to the steering column, I decided to hammer it back in.
And guess what. It was not the thing to do. Now I can barely shift into first or reverse. And I can't get the pin to slide back down, either.
Oh well, I live and learn. Just not backwards or in first gear.