Installing a K&N air filter is one of the worst things we can to do our engines. They don't filter worth a crap, they pass way too much dirt and fine dust. And as above our TJs don't have a MAF sensor.
probably running a heavy conventional gear lube, I have always like to switch over Redline synthetic in my diffs to reduce the friction loss and it usually nets me a mpg on the highway mileage.
Running a synthetic gear lube absolutely will not cause better mpg. What it can and will do is raise the temperature at which the gears run since synthetic gear lubes don't extract/sink the heat out of the gears as well as a conventional gear lube does. It's especially critical to run a conventional after installing new aftermarket gears due to the critical break-in process where keeping the temperature low is critical. New vehicles can run synthetic gear lubes with new gears only because their gear manufacturers pre-lap them so they don't need a break-in like aftermarket gears do. Which is why manufacturers like Revolution Gear, Yukon, Currie, Dynatrac, etc. either strongly recommend or require conventional gear lubes to keep their warranties intact.Spit balling an idea- how long ago was the gear change- I assume that you had some beak in time? I am not savvy enough on the gear set-ups if you can set those too tight that it would have increased drag.
