Ok, here we go:

I'm very sorry that you bought the GMC Denali and in all seriousness it is my least favorite bike on the planet. Please return it if at all possible. The derailleur is moving because of its cheap design and composition.

Here are cycling fanatics around Pennsylvania:

http://lmgtfy.com/?q=Ephrata%2C+Pennsylvania
http://wpwbikeclub.org/
http://www.lancasterbikeclub.org/

Well you see, cyclocomputers have settings for wheel diameter. You need to determine and input this wheel diameter into your computer for any kind of accuracy.

Here: http://www.sheldonbrown.com/cyclecom...libration.html

For future reference, Sheldon Brown, God rest his soul, is as close to a God among men as is possible in the cycling community. Please check his website (and the search function on this one) before asking any questions about cycling that other people may have ever had before.