Hi Mugsy. I suspect your ignition switch.
When the switch is in the "run" position, it seems to work fine. Power is provided to the ignition and the truck runs.
When the switch is in the "start" position, the engine cranks OK, but I suspect that it disconnects the power to the ignition on those times that it won't start.
Your screwdriver trick bypasses the flakey "start" position which means that the switch provides power to the ignition while cranking and the engine starts.
You have a voltmeter. Next time it doesn't start connect the voltmeter to the ignition terminal on the switch and observe what happens while cranking. If the power cuts out, you know the switch is toast.
