What kind of axle is on the 2001 dodge ram 4x4?

The 2001 Dodge Ram 4x4 used a Dana 60 front axle and either a Dana 80 or a AAM 11.5 rear axle, depending on the truck's configuration (payload capacity, engine, etc.). You'll need to check the vehicle's specifications or look at the axle itself to determine which rear axle is present.