2003 Chevy 2500HD 4x4 no fire

Did it run before you swapped all the parts?

Try spraying starting fluid into the air intake. If it starts for a bit, then it is a fuel problem.

Also check spark plugs if you can. At night you can remove a spark plug wire and hold it near a body metal part and see it spark. On cars with coils on each spark plug, you would need to use a voltmeter or some other testing device. But if not sparking, than that is the problem. (And it would do nothing with sprayed in starting fluid.)

Best is to get a factory service manual or CD/DVD from the vehicle dealer and follow the troubleshooting section. Or go to alldatadiy.com for the same thing on-line.