Juarezman

Hey guys, i just purchased a 96 f150 xlt with a 5.0, the truck turns on great. When its cold you can put it in reverse or drive, it drives good, but once it worms up, and you put it in drive it turns off, but if you push the gas and you go it will drive or if you put it in neutral it will stay on but as soon as you come to a stop, it will turn off again, Ive checked the spark plugs and the wires and there both were replaced by the last owner, they are new, what else could it be? thanks for your help in advance