A friend of mine has a 99 2500 with the 24 valve cummins. At times it wont start. If you would turn the ignition to start and crank it, it wont fire. Now if you back of on the ingnition switch towards run it will fire and run. Hmm, Maybe the ignition switch. Not. Replaced the switch and the key tumbler. Still nothing. Replaced the cps on the side of the motor near the starter, still same problem. Ocassionally, while running it will shut off also. Any Ideas?