My v6 dodge ram v6 3.9 is burning bet wen 8-12 mpg. What I have changed

tune up:

spark plugs.
ecm
spark plug wires
evap system and purge solenoid
air filter
oil change mobil 1 filter and oil
pcv valve
bank 2 fuel injectors.
distributor cap and button
both o2 sensors
changed crank shaft sensor
catalytic converter about 7 months ago.
fuel pressure is at right but the gauge fluctuates during readings about +5 or -5 of what the reading should be.
just got transmission to shift great and noticed a difference in power.
but every time i change something the mileage gets worse. When i change the ecm it was up to 16 mpg. but that was a year ago.

 

Is it burning oil?

 

It burns about half a quart every 5 months. But Today I did see carbon on the spark plugs. Not sure what that means. But do know carbon is by product of oil.

 

What brand O2 sensors?

Why did you change the PCM?

 

The o2 sensor are NTK's and I replaced the ecm because I was getting random misfires on bank 1 along with pressure transducer errors.

 

Have a look down your throttle body, see if you see any oil on bottom of the intake.

 

Don't see any oil. Could it be the fuel pressure regulator?

 

Only if it were leaking externally..... O2 sensor is the biggest factor when it comes to gas mileage.

Did you reset the computer after making all those changes? (just disconnect the battery for a few minutes.) Getting any codes?

 

I did a pc reset. Disconnected neg and pos for about and hour and reconnected it. The regulator is attached to the fuel pump in the gas tank won't be able to see a leak. But when I do a pressure test I get fluctuations.

 

If the regulator is leaking gas back into the tank, it won't effect fuel economy.