Now I know these trucks don't get good gas mileage. But here is the thing, is a Sport ORE with 4.10s it's not only allowed then my 2500 with 37s and 3.55s but it also gets worse (2500-12mpg, this one 6mpg) than my 2500.

I did the plenum, tune up, and timing chain. It just feels sluggish.

 

Should be able to do better than 6....... Something else is going on there. How old are the O2 sensors? Cat plugging up?

 

The engine might be running super rich. Look at the temperature and O2 sensor readings, they might give a hint.

 

Check your vacuum. You should be pulling 17 inches of mercury, more or less. If it's low, you might have a collapsed catalyst or rusted internally muffler. Unless you live near fields in which case you might have mice nests in the tail pipe. It could be other things but I'd check those first.

 

I did check them. They turned out to be good. I did get an evap large leak code

 

I will have to look into that, although vacuum seems to be good

 

Here is the scan data. Only thing I noticed if fuel trims are high and the rear O2 sensors is only fluctuating 0.20ma.

 

Wow. That's adding a LOT of fuel...... How old are the O2 sensors??

 

I had a car once that the fuel mileage tanked. I mean serious tanking. It went from 21 mpg to 8. There was a problem with one rear brake dragging the parking brake. You can check your wheels with a remote thermal thermometer and see if one is extra hot.

 

I had that problem on my 3500 someone over tightened the emergency brake and it was dragging lol. Forgot about that, will have to look into that