I have a 07 jku with 3.21's and 35" Nitto trail grapplers, very heavy tire and a 2.5" teraflex BB lift. But the rig has enough power to get me around. Right now I have no type of CAI or chip so Im getting 12 mpg, on a good day. You will be fine as a DD until you re gear

 

I am also running 35's on 3.21 and it isn't too bad. I've got the older 3.8 so you should be better off than me. Unless I am on the highway either level or downhill 6th gear is useless but overall it isn't too bad. I am hoping to regear next spring but in the meantime it gets me where I need to go.

 

Well I ordered my tires. Went with 315/70/17 Nitto trails on the stock wheels. Thursday can't get here soon enough.

 

2012 2dr Auto with 3.21 gearing. Have 2.5 teraflex lift with Toyo OC MT 35x12.5x18 with HD Monsters. Anyways... not that bad. I actually thought I had 3.73 because of it. I still want to go to 4.56 or 4.10 beacuse I just want that extra power! Right now Im getting about 14 mpg (not too bad, but stock was at 18-20). To each there own, but yeah, if you plan on towing anything, then gear up, or stay in 4th gear most of the time.

But absolutely get the ProCal. It is a must with bigger tires. Especially if your going from 29" to 34"tires like me...

Again, this is a 2012 3.6L
2011-under 3.8L is way different.

 

I would prefer at least 3.73's with 35's. 4.88's seems entirely excesseive unliess you plan to go to 40's, or just love putting fuel in the tank.

 

I have 3.8 with 3.21 gears and 35's. I don't mind it. I have superchips as mine is a 2010. I drove 6 hours to a jeep jamboree this weekend. And I drive an hour and half each direction daily for work. So. I like my gears

 

You must be in too high of a gear, or driving too fast for the new tires/wheels. Mine dropped 2mpg or less on highway with a 3.8L.

 

Maybe... but they sure are heavy tires! Mix between highway and city. Bit of a heavy foot too. All big factors...