starting problems

I have a 2000 Dodge 1500 p/u with 5.9L engine with 134,000mi. Some days it starts just fine and others it decides it won't work. It'll turn over but it won't sustain the ignition. I have to hold the gas pedal down for about 15min so it won't cut back off. When it does this I hear a clicking noise. I have told the Dodge dealership that works on my vehicle about this problem and they have no ideas. I have had the battery and alternator tested and both are fine. Unfortunately I am not mechanically inclined and I need help!