I just bought the car about 2 weeks ago, It is a 2000 Gt 4.6 with 46k miles andsince then it has done this about 5 times...
When I have the car in Park and then move it to Reverse or drive and dont give it any gas it stalles out ?? I'm not sure what is causing it, Mayb some Fuel system cleaner or something.
Anyone else have this problem at all ?

 

I'm not real big on automatics, but maybe your IAC ???

 

I just had the same problem on my 01 roush stage2. It did this for about a week then the alternator crapped out. Replaced it and no more stalling or surging of rpms.