Edward T is right on the money with his thoughts on tune up. I have had this Position sensor error on many occasions on numerous trucks. This is often caused by a bad coil on one of the plugs or even a misfiring plug. Anything that can change the speed of the crankshaft sensor relative to what the computer is looking to see. If you do end up changing the crankshaft position sensor, i recommend changing the camshaft position sensor as well.