My range gauge in the amount of fuel I supposely have dances around like no ones business, 173 miles to empty then 213 a second later! Anyone else's do this?

The range is never accurate. It more or less tells you roughly but yes it does change depending on your driving style

Range guage will definitely jump around just after a fill up. In the early miles of the predicted range, the driving style adopted, getting stuck in traffic etc will have a disproportionate effect on the reading as the software has only had very little 'sampling' to work on so tends to assume that whatever consumption you are doing at the time will be the same for the whole tank!!  As you tot up the miles on that tankful, the averaging of many more 'samplings' should see the range reading settle down to much smaller differences between readings shown.