Poor Fuel Milage 1998 Taurus

Mfg: Ford
Model: Taurus
Year: 1998
Engine: 3.0L code "U" Mileage: 125,000

City driving fuel economy has deterioated signficantly about 12 mpg (Highway speed 50mph or greater the fuel economy is great! Around 25 mpg).

My main concern is the LT FTRM2 reading is much higher than LT FTRM1 the opposite bank. Everything being equal they both should be reasonalbly close in readings.

I suspect a problem with 1 or 2 injectors leaking or possible OS2 sensors.

One more piece of information, as driving speed increases the LT FTRM2 reading drops significantly but it still is nowhere near LT FTRM1 reading.

Code Scanner reveals the following:

ENGINE SPD(RPM)1150
MAF(LB/M) 0.81
IGN ADV(DEG) 22.0
ST FTRM1(%) -0.8
LT FTRM1(%) -3.1
ST FTRM2(%) 2.3
LT FTRM2(%) 14.8
O2S11(V) 0.525
ST FTRM11(%) 1.6
O2S12(V) 0.745
O2S21(V) 0.535
ST FTRM21(%) 3.9
O2S22(V) 0.825
FRAME: -5 TM: -8.8

Any Ideas on where begin to resolve this issue. Car runs fine, plenty of acceleration, starts easy hot or cold