Edited because I saw you have done a regear.
Basically aside from an engine swap our getting a new jeep with a 3.6 your not going to get much better performance to the point that it will outweigh the cost. With the engine tuned and the regear done that's about as good as it is gong to get. Also looked at your profile saw you changed out to a cold air intake set yup. Those are a joke. The only thing those will do is make the engine louder and allow dirt to get into the engine. Also I have yet to see, outside of a high performance engine where those things do anything for the actual horse power.
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:thinking: allow more dirt into the engine? not sure what kind of filter you run but at about 150k miles the engine still running well. like anything else, you need to keep the air filter maintained and clean, personally I wouldn't run a stock paper filter for trail use and don't care for the oiled filters because in dusty conditions they plug up too fast. Any filter will eventually cause the engine to suck in the dirt if they are not kept clean.
I carry a dust boot for my filter, if I find myself in dusty trail conditions I can easily slip it on - does it work? not sure but when I take it off and see how much dust it has blocked I'm thinking it's helped.
for myself, the mods I did engine wise weren't for magical HP - it was all about the response and I can say they've given me what I was looking for - let the engine breath and get the most bang out of the spark.
to the OP - I'm sure you'll be told to install headers... stay away from headers, shorty headers create too much heat, not worth the cost and having to thermal shield everything to keep stuff from melting (ask me how I know)
I've talked to guys that run long tube headers successfully but not enough bang for the buck to make the extra heat and other mods needed worthwhile.
TB spacers do nothing, I've tried lol
having both a 3.8 and a 3.6 I definitely prefer the 3.6 ..but....I'm thinking it's the transmission that makes it so much better.. the 3.6 transmission gearing fits to the power band much better than what the 3.8 does. if there was a way to fit the 3.6 transmission to the 3.8 I'd try it.
As of now, I'm still saving up for an LS swap unless I break and buy a 2017 Rubi.