2.5 dhse auto stalling when moving gear wtf.?

HI,
Im looking for some advice I have a mint 2000 2.5dhse drives perfect until today. I started the engine as normal let it warm up. I then put the gear shift from P to D. The car then stalled. I nearly shat my self as I was infront of my work buddys and its an automatic. Anyway its happend 3 times over the last few weeks. I checked the tx oil its ok. there is no grinding from any gears she drives fine. im just worried it might brake down when im not near home or the wife has the car. there is no leaks smells warning messages.

any thoughts

T/F switch playing up then, especially if you've been off-road or very bumpy drive, might have moved slightly.... loose/corroded connection?

Silly question, Were is the tf switch, and what does it do. sorry I have not got a clue about engines.

thanks for the heads up.