What Tom said is pretty on point. Honestly, there aren't many people who know Libertys better than him. I've been on this site since late 2000s (even tho my join date is 2015, big lurker), and the reply I look for in every thread is from him, because his responses are knowledgeable and accurate.
The 3.7 has enough power to push 32s, steel bumpers, and full armor without an issue. I ran 32s with the stock 3.73 gears for almost 8 years, only recently switching over to 4.10s. Driving it now is night and day from the stock gears. While the 3.7 would get her around relatively well, on any hill it would be searching for gears, and around town I had to leave it in OD switching between 1st and 2nd gears (automatic). That being said, I've had more than one passenger say that the Jeep is quick, even one asking if it was a V8! Then I put in the 4.10s, night and f******g day from the 3.73s! If it was quick with overdrive on and keeping it in 1st and 2nd gears, then its downright fast now, for a jeep that is. I drive the hell out of her, hitting the redline daily, really letting her stretch and breath. If it had more power, then it honestly wouldn't be any more useful than what the 3.7l provides.
All that being said, nothing really touches a diesel. Low end torque is an off-roaders dream. If your pockets are deep enough, I bet you could squeeze one of those new Cummins R2.8 crate engines in there. Go ahead and hate on the idea everyone, but the new Cummins is a pretty damn nice engine.