It seems to get somewhat confusing as to what you might find under a GMC 1/2 ton. Even the factory literature contradicts itself. I've found one that lists the Spicer 45 as the 3.07 and the HO33 as the 3.90 depending on option, but another source that only lists the Spicer in 3.07 and 3.92, again, depending on option. Both were factory literature.
