I recently changed out my throttle body. My engine is a 3.7L and I slapped on a 4.7L throttle body. I also have a cold air intake, exhaust and programmer. I'm currently on my second tank of gas with the mod. My first tank was 20.02mpg (hand calculate). That first tank was 85 percent highway at very fast speeds. Prior, I was getting 17 city and 18.5-19 highway. Looks like the gain will be at least 1 mpg. I'll keep an eye on it over the next few tanks. A little more info about the throttle body... The stock one is 2.5 inches. The new one is 3 inches. The new throttle body pairs very nicely with the cold air intake since the pipe is 3 inches wide. The Jeep's performance has increased and not by a little, it's very dramatic!