After '04, All CTD's have the 11.5" rear. The '03 and '04's were hit and miss.
Stay away from the 4.10's unless you tow heavy all the time or plan on going with BIG tires. The 3.73's will be the best all around gear.
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'03 Black 2500 QC/LB 4x4, 6 speed, BHAF, 2" lift, black H2's, 35" BFG MT's, B&W turnover, Juice w/ Attitude, 5" str8 pipe, BD lift pump, spin on filters, Firestone bags
Ohio Coal Roller