Again...what was your MPG before you ever lifted? I guess what I'm getting at is, is it possible that your Jeep got substantially better than average MPG before you even lifted? I've seen some people claim they're pulling in the neighborhood of 24 MPG stock. Mine has never gotten over 20 stock, so I wouldn't expect to get over 20 even re-gearing.
Also, back to my point about leaving my gearing at 3.73's...my Jeep is lucky to see 1K-2K miles in one year. It just doesn't make sense to drop over a grand re-gearing for no more than it gets driven. I never argued that re-gearing wasn't beneficial...just that it's not required. And I'll still stand by that argument. I don't even have a problem towing a small trailer with a 700# zero turn mower on it with stock gears...let alone just driving it by itself.
If we want to drag this post back to that argument, I'll kindly point out that some of you want to give a blanket answer for all situations and circumstances. There is no such validation for that argument...other than because you say so. You take no consideration of the specifics of each person's needs or the variables in the equation, yet claim to have the end-all be-all answer for everyone. That is why I give you guys grief over it. I don't mind the SUGGESTIONS...but it's when you tell me it's your way or the highway, that's when I get chafed and make a stink. I truly appreciate everyone's opinion and offers of input based on their experiences...but it just bothers me that some people ignore the input from others, and pretend their opinions are the only ones that matter.
So to prevent any further distraction from the original topic, I'll leave it at that.
Back to the OP...anytime you add mass (heavier tires, custom bumper) increased rolling resistance (again, heavier tires) or raise a vehicle thereby increasing drag, you will lose MPG's. As suggested, re-gearing can help you overcome power loss, but I wouldn't expect to see a huge improvement in MPG's because of it. Especially since going to a shorter gear (4.10 vs 3.73) usually equates to higher RPM's at highway speeds, which equates to more fuel being burned.