Your problem is being caused by a leaky power steering switch.
The switch develops a leak, which causes power steering fluid to seep into the engine wiring harness. The seepage eventually finds its way into the front O2 sensor, which then shorts out. The engine computer then starts reading a lean condition, and enriches the fuel/air mix going into the engine to compensate. However, since the shorted O2 sensor never responds to the extra fuel, the engine computer keeps shooting more and more excess fuel.
Replacing the O2 sensor by itself will not help matters, as you may have guessed. The seepage will have about a week or two to short out the new O2 sensor, then you will start seeing the same problem again.
The cure is to replace the leaky power steering switch (it's near the power steering pump), spray brake cleaner into the wiring harness until it drips off from near the front O2 sensor, let dry, and replace the front O2 sensor again. All of these actions must be completed, or you will see another recurrence of this exact problem.
56041335AA - Power Steering Switch - about $20.00 or so at rockauto.com
I troubleshot this exact same problem on my friend's Dakota (now my Dakota). He took it to a number of dealerships over a course of 2 years, and none of them could fix this problem.
2000 QC with 4.7L V8, 545RFE transmission, Polished/Ported Cylinder Heads, Bosch +4 Plugs, HO Cams, Mopar beehive valvesprings, bwdakrt 65 mm Throttle Body, Fuel Delivery mod, Magnaflow Hi-flow cat, Dynomax Cat-back, Trans-Go Shift Kit, JGC Fan conversion, no stock engine-driven fan, Ceramic front brake pads, Power Slot Cryo rotors, Goodridge S/S brake hoses, PLX M250 WB AFR gauge, 2004 Mopar fuel injectors, JBA Ceramic coated headers, coolant-based intake heater