I recently bought a Superchips 3870 from Kolak (great price, fast delivery, and responsive guy).
For reference: http://www.superchips.com/Store/JeepFlashpaq.aspx
Since there are so few 08 4.7's out there, I thought it'd might be helpful to folks on the fence.
It has a myriad of options that I haven't yet played with. For example, out of the box, I can control up shift/down shift, load shift RPMS, tire size/speedometer adjustment, fan-on RPMs, idle speed, CEL codes, ect.
What I have tried is below:
91-Performance (not tried)
Towing (not tried)
Mileage XS (tried)
Crawl/OffRoad (not tried)
On all of these, the effect I noticed was that when I just lean on the throttle, the engine comes alive instantly. I think/guess this is a result of me giving the throttle 5%, and the ETB actually opening the throttle a lot more. Also, the shifts happen at much more reasonable times. The vehicle isn't always trying to get to 5th and do everything it can to stay there (stock).
WOT performance is marginally better than stock. Everything below WOT is much better. It's extremely responsive and well rounded and, as I mentioned before, the shift points are in the ballpark of where they should have been from the begining. It almost has the acceleration of the 93-Octane tune, but is not too aggressive with ignition timing and makes it easy to maintain a constant speed
. For example, I'd have to put the throttle past 75% while stock to get the thing to downshift while going 30 mph. Now, it does it at almost half of that. However, when I am going 30 mph, and give the gas a few percent throttle, it stays at 30 mph. It has pretty even acceleration at all speeds and loads. This one is my favorite. It's fast, easy to drive, and fun. I'd recommend this tune for city driving.
WOT performance is a little better than the 87-Octane tune. Everything below WOT feels like the jeep is trying to get to the top speed. It turns your accelerator into an ON/OFF switch. Holding a constant speed in the city is actually pretty tricky. I attribute this to the ignition timing advance. Just putting pressure on the accelerator, the front end lifts up and it tries to accelerate. As you can imagine, this invites speeding tickets, but it's fun. I took the jeep into the woods with this tune (not intentionally) and it makes driving in 4-Low very hard. Everytime I run over a rock or log, my foot would bounce, hit the gas, and all 300-350 hp would come out at once and launch the jeep forward. This tune makes trail-foot dangerous.
Feels like stock with the exception of faster throttle response. Worse WOT performance. I had to merge onto the highway on the way to Buffalo and actually started to get a bit worried. The on-ramps in Upstate New York are made for sports cars.
There was a mileage increase on all tunes. However, I have to make the disclaimer, that I was discovering the advantage of the front air-dam at the same time. So my experiences have two variables. The front air-dam makes a huge difference in mileage (no skid plate).
According the the mileage computer cruising Upstate NY hills at 55 to 65 mph for about 3 hours each....
18-21 mpg w/air dam
Didn't pay attention
20-22 mpg w/o
18-20 mpg w/o
air dam, 20-23 mpg w/
air dam (I don't undersand why it's so high, better atomization of 93 octane?)
These numbers are based on me babying the gas to get the best mileage. Real world numbers will be less.
Summary: Buy one, it will pay for itself eventually. The major improvement over stock is the instant throttle response, but not neccesarily faster quarter mile times. It makes driving this heavy beast more reasonable. Also, it's great to reprogram your spedo with bigger tires/gears and read and clear CEL codes. The claims for my engine is something on the order of 50 HP increase. I believe it, but it's not a 50HP increase over peak power. It's probably 50HP over your weakest point in the map (hence the even acceleration).
If you have multiple jeeps, you have to flash one back to stock to flash the other.