Re: Can someone please explain the "tuners" for the JGC
Tuners come in a variety of flavors, but the main categories--and these are my terms--are piggyback units and reprogrammers. They're not difficult to install, though it's important to follow the directions closely. Failing to do so can render your vehicle an inert lump of steel.
I've used reprogrammers--specifically Cobb AccessPorts-- on turbocharged vehicles (Subarus and BMWs). In those applications, you can realize huge increases in horsepower and torque. The Stage I program I currently have on my 535xi yields increases of over 30%. But this type of increase comes largely from bumping up boost levels (plus adjusting timing, air/fuel ratios, etc.) and is simply far beyond what you'd see in a vehicle that's not turbocharged or supercharged.
On normally aspirated vehicles, these tuners typically yield much less impressive increases, despite some very inflated claims from their manufacturers. You might eke out 10-20 hp. on a hemi, but I'd question claims much beyond that. Of course, there can be a bit of a cumulative effect from adding a CAI, exhaust, etc. However, it's generally going to be less than what many people on discussion boards claim . . . and it's not simply a matter of adding 10 hp from a tuner + 8 hp from a CAI + 15 from an exhaust and yielding a 33 hp gain; the cumulative power gains are often less than what the individual components would add up to.
Where a tuner can help is with issues of throttle response, like the lag you note. With a drive by wire throttle, the CPU makes certain assumptions as to how the vehicle should respond and sends its decision to the engine. A tuner can alter the response of the CPU, telling it to adjust fuel flow, timing, etc. to achieve greater responsiveness. Also, sometimes the tuners do little more than alter how much throttle is applied over a given range of gas pedal application. This makes the vehicle feel more powerful, but it's simply a matter of applying more throttle with less pressure on the accelerator.
I'm not by any means an expert when it comes to any of this, particularly Jeep products, but I wouldn't expect a huge performance increase with a tuner. You might eliminate enough throttle lag to make the driving experience more pleasurable and you might bump up your horsepower/torque by a few percentage points, but you would need to make more extensive modifications to effect a serious increase in performance.