Decreasing Gas Mileage in Dakota???

Thanks for the input guys! I really appreciate it.

a year or so ago, I swapped the old factory plugs with the same exact ones and gapped them to whatever the spec in the FSM called for (0.040" i believe). Some of the old plugs had as much as 0.065" of a gap. I'm pretty sure none of them are crossthreaded. I didn't use a torque wrench. I just snugged them down like I always do. Since it's easy, I think I'll pull a couple and see what they look like.

I also thought about the whole ethanol thing. There is ethanol in our gas here in California, but I'm not sure if the percentage has changed recently. I don't believe so. I think we've got 10% for regular pump 87, but I'll have a check.

So far, my list of things to check includes a couple plugs, ethanol percentage, and any trouble codes.

Is it possible that a faulty O2 and/or coolant temp sensor may NOT throw a code?

Thanks again guys.