1998 528

I have a 1998 528 that has had the transmission download done to it. After the car went through some deep water on the freeway about 6 months ago in southern Louisiana the transmission started shifting hard from 1st to 2nd, not all the time but enough to be annoying and concerning . While driving in the neighborhood 2 weeks ago it went into "safe" mode, the light came on on the dash and the engine revved a bit while the transmission seemingly slipped. I spoke with a friend that many years ago was a BMW mechanic and he said the transmission probably just burped and to disconnect the battery and reset it. Instead I started the car the next morning to take it to a shop and the light had reset and it was shifting smoother than it had for some time, however it has done it one more time, this time we turned it off and back on again in about a minute and it reset itself and has worked fine since. I am wondering if perhaps it is a sensor that may need replacing as he suggested it may be as well...any ideas?

What's a "transmission download?" You need some expert diagnostic help.

You also haven't told us how many miles are on the car, nor what its maintenance history is. Have you owned this car since new?

I have not owned it since it was new but knew the previous owner. The vehicle has 174 K miles on it and is taken care of very well and driven by my wife who babies it.