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[aposak]

Thanks for the suggestions. I tried swapping the fender solenoid with a new one, and the starter solenoid with the one from my old starter. Neither seemed to help.
After that, I did some more testing with the switched output from the fender solenoid. It only has 2 wires: the one to the fuel pump relay, and the one to the starter solenoid. If I left only the fuel pump relay connected, it behaved properly. When I turned the key to START, the fuel pump would cut on, and cut off when I let off the key. When I put only the starter on the solenoid, it still kept cranking after I let off the key, and even after the truck was running. However, when I set it back up to the fuel pump only on the solenoid, then touched the starter lead to the always hot side of the solenoid, it fired up properly. Those tests seem to be taking me in different directions as to what is wrong. I also tried pulling the ignition switch wire (small terminal, with the boot) off during one of the runaway crank times, but that didn't stop the cranking. Didn't think to check it with the fuel pump only, to see if that would actually work, but I will tonight.
Any thoughts on what could be wrong, or additional tests I can do? I'm trying to avoid dropping another $200 on a starter, since I already dropped that much on a new one this spring.