So I just did my oil and changed the oil filter and my mpgs dropped below what I usually get. I was getting between 13 to 13.5. Now I'm getting 12.2 to 12.5. Any ideas why or what I can do?

 

First, how are you determining your mileage? Second, it will vary. Weather, speed, terrain, driving style, 4WD use, etc, will all change the mileage. Third, is your odometer properly calibrated (have you programmed the Jeep for tire size, if you changed it?)? Looking at all of that, here is what my gas mileage numbers were for my trip to Moab last week. All are hand calculated, and my Jeep's odometer has been confirmed as properly calibrated:

12.6
13.6
17.4
15.2
10.6
16.5
14.3
13.8
9.6
15.2
15.9
15.7
11.1
11.9
12.5

You can see that my mileage was all over the map. Besides the days spent four wheeling (which explains that 9.6--Tower Arch Trail, and Fins and Things), there were some very windy days and some days that the weather was perfect and my speed was mostly in the 60 MPH range (no Interstate travel). And, since I just know you're going to tell me that you drove exactly the same trips, in exactly the same weather conditions and exactly the same driving style (LOL), maybe you should track it a little bit longer to see if you have a real problem, or you are just experiencing the vagaries of calculating fuel mileage.

 

I'm going by the odometer reading. All highway and road travel no 4wd. Mostly the same weather. Ill watch it longer. And my speedometer didn't have to get recalibrated my sensor for tire pressure needs to be.