If you’ve got no issues with it, and you’ve been taking good care of it, then it’s likely either the sensor is going, or there’s a problem with the wiring.
Have you been using genuine Honda transmission fluid? I’m not sure if the 99 model is picky, but I"m pretty certain some other years are very picky. If you’re using the local drive-in and change it chain, I’d recommend not going there again, and use either a good local mechanic, or the dealer. Both will likely be more, the dealer the most, but it’s just not worth losing an engine, transmission, or any other parts because of their failure to follow simple procedures. There are stories everywhere about them messing up car after car.
You didn’t tell us what transmission it is, although I’m assuming (bad, I know) it’s the automatic, and you didn’t tell us which engine (V6, or I4?). So it’s a guess.