I have a Set of Shop Force detail buffers both a 10" and a 3" that include pads and an extension cord. Neither have ever been out of the box. Looking to get a red bull for trade....seriously someone come get them.
the front end/steering wheel vibration is warped front rotors like everyone said. If you're feeling it in the pedal as well the rears are warped as well
try Braden or Chase over at Fleece Performance Engineering in Danville, Indiana. They can hook you up with a turbo and a tune and specialize in duramax's.
http://www.fleeceperformance.com/Default.aspx