it sounds like you are burning oil by the description all right. (black Blob) That's the problem with buying a vehicle with a manual transmission these days, the cat hides problems like this. Personally I'd start looking for a 4.0 to swap into it, since it will give you better fuel economy end low end torque. The 2.4 doesnt shine until its spinning above 3 grand. however that means swapping out the PCM as well as all different wiring between the two. When I bought my 06 with the 2.4 it was with the intent to install a bored and stroked 5.2 or 5.9 when the 4 cylinder dies, but it hasn't even belched yet...
And yes the 4.0 will give you better mileage due to higher low end torque, especially with the 6 speed. you will do less down shifting and will be using 6th gear a lot more. The one thing I would do, is add an old fashioned vacuum gauge so you can see when to shift if you do put a 4.0 in it. You will find quite a bit of overlap range between two gears, and a vac gauge will give you a better idea of when to shift than just engine speed, since the higher the vac for a given speed will supply better engine performance in most instances.
We like to hear the reasons why people feel the cause is what they think it is for a couple reasons, the first is in case of a mistaken diagnosis, and the second is if someone is having the same problem, they get a quick start on their work and can learn from what others have done. If nothing is learned, and a quick repair is just put in place, we don't really get to know the in's and out's of our jeeps, and are left SOL when they go down on the trail.