2005 Ford Explorer sometimes stalls after running to warm I

I had the truck since dec 2009 I always warm it up before leaving for work. I backed out of my driveway and went down the road and the truck just shut off and would not start back up I waited a few minutes and it did start but felt like it was idleing or running rough
its happened 3 times now and I have had it down to the dealer and they can't seem to fix it
let me know what u think

angie