55-60mph. i think 15mpg is normal though...id love to hit 18+ but im not too sure how those ppl are getting that (esp those with larger lifts and tires than i). but then again, the dude in that clip i posted is getting 36mpg!!!!!! lol
Did you recalibrate your speedometer? That would make a difference. 15MPG is what I get but then I push my Jeep a little and get it up to 70mph on bursts. I also do a lot of short (6 mile) trips during the week.
I get as low as 14mpg but I average 15mpg. That's calculated over several years. When I was driving on the highway more (40 miles), I'd get 18mpg though.
Honestly though, if you want to get better gas mileage you will need to reaccess your priorities. Things like, if you're driving offroad enough to need 33x12.5R15's. Skinny 33's or 31's would probably help a lot. Wider flares, crawler fenders, and a lot of other stuff that help offroad will really hinder your mileage as well.