If the ignition switch is the culprit, then you can recreate the failure without starting the truck. Unhook the start wire from the relay and hook a test light to it. Turn the ignition to start, and see if there is voltage when you release the key back to the run position. Also, you may see power before actually turning it to start. If you do, then either the ignition switch is bad, or you have a short in the wiring circuit. You can troubleshoot this without constantly starting the engine by disconnecting the coil wires. This way the engine will not start, but the cranking problem will still be there. If there is no power going to the start wire but the engine continues to crank, then it is definately a sticking solenoid.