engine replacement

I'm confused, you show a 2001 Jeep Grand Cherokee with a 4.7 V-8 and your asking about a 5.2 V-8. Which engine do you have? If you have a 4.7 V-8 you'll get no better gas mileage with any other engine. Sorry

None of the Jeep motors really get good gas mileage. I work at the dealer and even the 4.0 in some of the jeeps only gets about sixteen. My 4.7 in my Cherokee gets around 15.6 so really no help with any engine. I have not seen one with a 5.2 ever. The only option I can offer is to trade it in on one of the new V-6s on the market but that engine will not fit in your jeep, have to buy a newer model with that engine in it.

i own 4 grand cherokees, all get about the same for gas mileage 2 of them have the 5.2l 318 and one has the 4.0 straight 6 which gets the same mileage as the v8's and the last one has the 5.9l 360 which gets a little less than the others but it also has the full time transfer case in it. over all they all get about 15mpg with 4.5 inches of lift and 33x12.50x15 tires on all 4 jeeps. (all 4 have been re-geared for the tires)