I ended up going with the True Flow XDI. The way I see it, I'll be regearing next so I can upgrade my tires from stock to 34's or 35's. However, that's a long ways away considering how much it will all cost. Thanks for all of the advice.

 

These are really two totally different aspects of performance and efficiency that are being addressed, so dependent on your objectives, one doesn't displace the other.

For the most part the way these vehicles come out of the dealers lot or off the line they are under geared. Add in, as a lot of people do, a lift, some larger tires, perhaps a bumper or two and you have created an issue that can only be reasonably addressed by moving to a steeper gear set. That in itself doesn't do anything to improve engine efficiency and performance.

Adding things such as a CAI/drop in high flow filter, headers and exhaust does increase engine performance and efficiency. However, it should never be looked at as a way to displace the need for a steeper gear set if one exists. If all the stars align and with a system approach to upgrading the intake/exhaust there is the potential for nearly a 10% increase in power/efficiency. Conversely if the objective is to get more power to where the rubber meets the road, a gear set swap from 4.10s to 5.13s doubles that and it's a very likely scenario for a guy who has an automatic transmission and newly installed 35s.

Simply put, you can't correct the issues that surround a 35s upgrade and an automatic transmission by intake/exhaust upgrades, even rolling in a programmer. That is where so many have found failure and even more so when they thought a single intake/exhaust component was going to whisk their underpowered issues away. Not that there wasn't improvement, but just a band aid to try and cover a gaping wound.

For my purposes, with a 6 speed, 3.73s and a long commute, my goal was to be able to maintain speed on the highway flats and find efficiencies while I was often spending more than a $1,000 a month on fuel. Certainly added performance was a want, and added engine efficiency was always the means for justification. My upgrades enabled me to exceed the EPA estimates by 20% on stock tires and my needs for additional power weren't that great, living in an area that's a couple hundred feet above sea level and I can drive for two hours in any direction before I need to meet a 100 foot increase in elevation.

While moving to a steeper gear set is certainly in my future, I have never had the immediate need that someone would face with an automatic transmission. My overdrive gear is already 20% steeper than an automatic (using like differential gears) and way in excess of this comparing first gear. When I went to 35s with the full intent of re-gearing I went on a 1200 mile trip to the coast through the highways of the Allegheny mountains and maybe needed to downshift a half dozen times each way. That totally changed my ambitions, and set forth a desire to run 37s which is a much bigger project.

That said, I believe there needs to be some goals set before determining ones path. There are a variety of needs different people have and different paths to achieve them. As a general rule of thumb all the programmer, exhaust and intake upgrades aren't going to address what a 5.13 or 5.38 upgrade does for the automatic transmission user. With a manual transmission, you just have a little more latitude based on 50% more gears and a steeper transmission ratio out of the box.

 

I will add... I purchases a K&N for my 08 Unlimited and I make several 6(+) hour trips per year and I don't there was any performance or mileage advantages... I truly believe I get better gas mileage in stock mode. I currently have an 09 Unlimited and will never upgrade the air filter again, in any vehicle I own in the future... just my 2 cents.

Good luck with your decision.