Okay so I have a 03 Chevy 1500. It has 5.3L v8. I was driving down the road and went to pass someone and gave about 3/4 throttle and you just fell on its face. I took it to a dealer to diagnosis it and they say 2 coils on cylinders 4 and 6 were bad and needed plugs and wires. I changed that and still nothing changed so I took it to another mechanic and he ran some more diagnostic and its still throwing the same codes? Any ideas? It has no power and spits and spuders. I've also tried the fuel filter and checked the pressure on the pump, no problems there. Just want to know if there's any thing I should check before I take it to a dealer and waste a lot of money.