the 03 ram pcm has an upstream and down stream 02 sensor.
the 04 and up rams have 2 upstreams and 2 downstreams.
I have a 69 barracuda with 5.7 from a truck, 6.1 cam, tti headers, factory efi, 04 ram pcm, B&G flash, 28 tall rear tire, tko600 with .64 overdrive. speedo has been verified, and adjusted with new gear in the trans.
At 70-72 mpg car got 24 mpg all highway miles.
i doubt hooking up the rear 02 sensors will show a fuel mileage increase.