I suppose it could be the ignition switch, my first suspicion however, would be the crankshaft position sensor. But your symptoms are a tad different. When the CPS goes out in some cases it will just outright shut off or stall and might be a little difficult to start back up. In some cases it will start right back up. In other cases, it will shut down or stall and take forever to start back up.
The reason for this is that the CPS provides two signals. The first is for RPM which also ties into the traction control which is why some will see their tachometer go to zero and the TCS light come on (indicating traction control is off). The second signal is for the ignition and tells the ICM (Ignition Control Module) when to fire. If the ignition control portion dies it can just shut off like you turned the key off and in some cases it will have to sit for a long time before it will restart, but not in all cases.
If the tachometer signal part dies, then it may or may not stall but it will probably turn off traction control and your tachometer will read 0.
With the symptoms you are having, I believe your CPS is on its way out for good. If it were the ignition switch I would think you would be having trouble with some accessories, like the radio not working, the DIC turning off or not having all the fan speeds on the blower.
Hope this helps out some.
