Here's what I know: Year, Make, & Model: 2004 GMC Sierra 1500 Ext Cab 4x4 w/ 96" Bed Tire size: 315/70R17 Original Gear Ratio: 3.73 (RPO Code GT4 = Axle Rear (DUP WITH 5 X 1) 3.73) Desired Gear Ratio: 4.56 Number of Cover Bolts: 10 bolt (11 inches wide - i.e. has GM 8.2 or 8.5 ring gear diameter, but not sure which) Transmission Type: 4L60E Engine Size: 5.3L Desired Highway Cruise Engine RPM: ~2000 Number of Wheel Lugs: 6 Suspension Type: Independent Front Here's what I need to know (ideally without any disassembly, as I'm merely information gathering in order to cost out parts) and don't know how to find out: Axle spline Count? Actual Ring Gear Diameter (8.2" or 8.5")? Number of Ring Gear Bolts? Dana Bill of Material Number or Tag Numbers (if applicable)? Standard or Reverse Rotation Front Ring & Pinion? Axle Bearing Outer Diameter? Can anyone point me in the right direction(s)?