TRACTOR FIXED. Sorry for the long time to post fix. Anyhow, dealer wanted $200 to pickup and another $200 to return tractor when finished. I figure $400 out the door for a warranty repair on a factory defect was not a very good deal so I sprung for the factory repair manual instead.
So... Got out and braved the weather today and worked on it. The problem was the throttle position sensor feedback voltage was not posting correctly. The factory specification for the throttle position sensor voltage at idle was .6v - 1.2volts. The Deere computer has the ability to display sensor readings in real time and a voltmeter is not even required. In fact, in order to use a voltmeter, a seperate breakout box needs to be purchased. I opted to use the dash display option. At idle setting, it initially read 0 volts, definitely no good. I wiggled the connector for the TPS and got .6v. Hmm, perhaps the connector has an intermittent? Anyhow, while the voltage at .6 volts was just barely in range, I could see how the voltage could drop below that minimum voltage threshold during operation and trip the error code. I decided to adjust the TPS to provide .9v during idle, the mid point of the low speed range. To do this, you merely loosen the two nuts holding the sensor in place and rotate the sensor to where it will post the correct voltage -- lock down the nuts and done. Restarted the motor and operated it for a bit and no more code. At this point, it appears to be fixed and it costed me a little under $100 for the service manual, a far better deal than the $400 the dealer wanted.