Will a 62MM throttle bosy give me better performance?

I have been thinking about getting a rebuilt 62 MM throttle body. I am mostly hoping to see better gas mileage from the switch. My 99 XJ has 113,000 miles and just want to see an improvement. Will this be a waste of money? Is the a way to adjust the TPS or IAC?

The computer controls the fuel mixture so I doubt it will make a differance by it's self.
You should be getting close to 20 now. A heavy foot will quilcky lower that to 14-16.

I have noticed if I am driving around and stop at a store for 10 minutes. When i get back in the jeep and start it it idles fine. As soon as i take off it will stmble and bog down for a second. once it back fired a little. Then after about 10 seonds of doing that it seems to run fine. aLWAYS HAPPEN WHEN THE ENGINE IS WARM. Any clues?

Need new plugs and a de-carb and clean the TB and TPS.