Yes sorry bud..auto correct on my phone kills me...back 2 cylinders (4 plugs)

 

I'd suggest hooking up an ODB-II scanner and make sure all sensors are working (they don't show "inc" on the display), especially the O2 sensors. Then I might pull the sensors to make sure the previous owner hasn't hooked some sort of "cheater" to them. A bad catalytic system could cause bad mileage, but the sensors should pick up a bad CAT if they are working properly, and they should be throwing codes if they aren't working properly.

All of that is in addition to what has already been mentioned. I get 13-14 around town easily and close to 19 on the highway and am also bone stock, except for exhaust, but I was getting that before changing the exhaust.

And, by the way, if your O2 sensors do show "inc", that could mean they aren't yet reporting anything that could possibly be wrong. It's possible the previous owner disconnected the battery, let everything reset, and a drive cycle hasn't completed yet - so you wouldn't see any emissions related CEL's.

 

Yeah i always get ahead of myself on here. Lol. No big deal i was just making sure. Do what Hemi Greg said, if you dont have a scanner your local parts store most likely will