At risk of sounding like Carnoobie/GHT/Technologs ... Weekend before last, I did a pretty big (for the Jeep) round trip on it. Put about 300 miles on it in one weekend. It's a 2000 Cherokee 4.0. On the return trip, I decided to tour some storm damage along the US20 corridor in CNY. They received some "straight line winds" even though a lot of people saw a tornado. For anyone that has ever drove on US20 through Central NY- it's a lot like this. You go up the steep hill, you go down the steep hill, you go up the steep hill, you go down the steep hill. I had to bring back some junk, tools and other stuff with me. Easily had a few hundred pounds in the back. It managed to squat the rear end a few inches. Anyway, on a lot of the steeper hills, I found that it wouldn't unlock the torque converter. So I had to manually force it into 2nd gear. Was pulling a lot of the hills at 3500+ RPM. Toyota built a great transmission, but the shift logic on them is strange. My kickdown cable is adjusted to be a bit over-active to get higher line pressures. No reason it shouldn't have kicked down ... First thing I noticed when I got back was how smooth the engine was running. The last few times I have drove it, it has idled very very smooth. There isn't a pronounced misfire, but it's just a bit rough at times. Mostly, the Jeep does short trips to work (8 miles) and back, or random towing and hauling. Longer trips are reserved to the car. My guess is the high speed operation may have cleared out the injectors a bit, cleaned off the spark plugs and got the cat nice and hot to burn out the crud that may have been starting to accumulate? Even more surprising - the gas mileage was 19.75 calculated by hand!