2003 Ford Windstar moving mystery

Hi, my van recieved 2 new front tires on sat. And then I drove it a couple of times over 24 hour period. I pulled into my garage at 4:30 and it was fine and when I went out at 10 to run errand. The van would not change gears. The parking light comes on when it's in park and the brake lights work when you put it into reverse. It hasn't been doing anything different lately except idle alittle too low, it hasn't stalled out but it sounded like it a couple of times.I had my "car guy" that just happens to live across the street and he checked tranny fluid and it was okay. So now we are perplexed, and confused. Although it probably is a coincidence about tires and tranny, but it would be better for me if they just knocked something off or something. Do you have any ideas what this could be? I like to have some sort of language of the possibilities so the garage doesnt get all technical on me. Thanks so much for your help!