2002 express 3500 no crank/start

I have a 2002 express 3500. Has 185000 miles. Has been giving some trouble starting, was like an hour from home and turned the key and nothing. So I jumped the starter( had done this before and it worked) and got nothing.
Now I have no power to my dash.
I have replaced the starter, the battery, ignition switch and relay. Using my old ignition switch I can jump the red wire (power all the time) and yellow (starter wire) and get the engine to turn over.
Using the same red wire I can cross the red/white wire (run/start) and get the dash to light up and again the engine will turn over but not stay running.
I have traced all the wires I can without taking the entire van apart and nothing seems to be intact. All fuses are good (replaced some but none were bad) .
I have no change in any gear so I have eliminated the park neutral switch.
I also have no power at my ignition fuse (under hood labeled 10A IGN-E). I think my problem has something to do with that fuse and/or the red/white wire.
I am working on getting an OBI to test my ECM and see if that tells me anything but I am at a loss as what to do next.

Welcome to AF, security lite on? Truck ever under water? Seem to remember that the engagement and gear position of the ignition switch and key cylinder is critical.

Try disconnecting the battery negative. Unbolt the electrical center look at the bottom. They use salt on the roads in Ohio you need power to the ignition switch. As Max suggested most of the GM's I've worked on had a rod from the ignition switch to the key cylinder. I've seen bent rods and the switch not mounted properly. You may need a tamper proof set of torx bits to adjust it.