1999 Ford F-150 F-150 in need of a miracle

I have a 99 F150 that I bought 2 years ago used. This problem Im having started occurring 1 week after I bought the truck. All my luck the place I bought the truck from went bankrupt and closed their doors. Anyway here is the problems its having. The Rpm's will go up to 4-5 grand out of nowhere, and then go back to normal. It will do this under any condition cold hot rainy clear. I will be at a stop sign or red light and it will rev up and lung forward sometimes. So Ive had to stand on the brakes when I stop so I wont cause an accident. It will also just completly shut down while driving normally down the road. Ive been to the ford garage 4 times and they dont have a clue of whats wrong. They have checked the egr, Ive replaced the alternater because they said that was the problem. Changed the fuel filter. Before when it would die while driving down the road I would just put it back in neutral and restart. Today it wouldnt restart. Just had to tow it back home. It cranks over great and I am getting spark from all cylinders, but when I can get it to start up it will only run until it gets warmed up and then dies out and you have to wait awhile until it will restart again. Ford mechanic said he didnt know. Said my best bet was to wait until whatever it is finally gives out then Ill know what it is. Well Im at that point now and I dont have the money to take it to a garage. If you could give me the answer or an idea of what to do I would appreciate it highly. Thanks