The check engine light came on, and once I had slowed down, the engine wouldn't get up out of second or third gear. It has happened to me before (different car

The check engine light came on, and once I had slowed down, the engine wouldn't get up out of second or third gear. It has happened to me before (different car years ago). The engine ran fine, happily got between first and second, and had no problem with fifth while we were on the highway. It was only after the light came on and I had to slow down to turn on the road to the place we were staying at that it started to struggle. And sure, I could have driven it, but it probably would have been a two or three hour drive topping out at 20mph... hence the tow. Given that O2 sensors aren't exactly expensive to replace, it seems like an odd scam.