[ridjazz]

One year I drove to Daytona from Chattanooga with 37s on 4.11 gears. I got about 11.2 MPG avg for the trip. While there I purchased a RIPP Supercharger and installed it in one day. (I planned this out). I drove home in 5th gear at 17.5 MPGs. 6th gear the RPMs were too low for the power gain from boost. In 6th for a while I averaged 12.5 or so.
I later regeared to 4.88. I drive interstate daily running 80 in 6th at about 13.5-14.5 MPG. If I go to work on the highway and keep speeds at 55 or so I run about 16.5-17. This is in the mountains of Tennessee. with 37” tires and 4.88 gears I run 80 at about 3000 RPMs and the throttle is barely pushed. But based on the math in low 4 I am still running the same crawl speed as it was when factory.
In short get the supercharger. Realistically the sooner you get it the more you get out of your money. I will have to own the Jeep forever for fuel savings to be made up, but there is something to also be said about having a vehicle perform the way you want it. A weak vehicle gives you three options in maneuvers. Brake, turn left, turn right. A strong powered vehicle adds the option to accelerate. Sometimes that’s better when it’s an option.