These apply to ALL 99-06 Chevy/GMC Full-size trucks and SUVs
Here are the bolt-ons that WORK
Most handheld tuners are a waste but if you must have a handheld tuner for some reason go with the Diablosport Predator tuner it can do more than any other tuner out there at this time. A handheld tuner contains a generic tune that works for everybody, but is VERY conservative, especially for the performance-oriented individual.
A mail-order tune is much better than a handheld tuner, but isn't nearly as great as an in-person tune. It is still a generic tune that works for more than one person, but not quite as generic as a handheld tuner. A mail-order tune is a tune that is much more aggressive than a handheld tuner, but not as aggressive as the dyno tune for obvious liability reasons.
A dyno tune is the best of all tunes. It is the most aggressive out of all of them and with a competent tuner anything can be changed or done. A live street tune can be done by an experienced tuner also and while much better than most other tunes, it still cannot extract all the HP/TQ out of your truck. However a street will achieve the best part-throttle, everyday driveability, hands-down.
Another option available for the advanced enthusiast is tuning software/ laptop. This is the most accurate way to tune and can be more expensive than other options to start with but after a while of not paying for retunes, it pays for itself many times over. This method of tuning requires logging data from your trucks PCM and analyzing the data and determining the changes needed to optimize performance. This method of tuning requires extensive knowledge of the truck's PCM, otherwise possible engine failure can result.
2. Exhaust - Headers
Headers are a very high-flowing exhaust manifold. Headers can be divided into three categories: short tubes, mid-length, and long tube. Long tube headers are the best, with mid-length headers in second, and shorties in last. Longtubes (LTs) provide the most HP available out of headers while sacrificing a small to unnoticeable loss in TQ. Mid-length (Mids) headers are a cross between the long tube header and the shorttube header. they provide great gains in HP, without sacrificing TQ. Short tube headers (shorties) are a header with short enough tubes that you can retain stock catalytic converter location, necessary for emissions testing in some areas, however they provide little to no gains.
When deciding on a certain header after deciding on the type of header, you now choose the material it is made from. Some of the less expensive headers are made of mild steel (ceramic coated and uncoated), while the more expensive and higher quality headers are made from stainless steel (ceramic coated and uncoated). Over time, uncoated headers will change in appearance. Mild steel versions will eventually rust through the primaries, while stainless steel versions tend to develop a blue hue to the primaries due to heat cycles.
Also when choosing a set of headers, look for equal length headers, they help scavenge the exhaust better.
3. Exhaust - mid-pipe
The mid-pipe connects the exhaust manifold collectors to the rest of the exhaust system. Different mid-pipes are used for different exhaust setups.
You will not get the full benefits from an aftermarket/custom exhaust without some sort of mid-pipe/crossover pipe. You will have poor, unbalanced flow among other negative things.
For a single exhaust setup, a Y-pipe is used. For a dual exhaust setup, either an X-pipe or an H-pipe can be used. The X-pipe favors top-end HP. The H-pipe favors bottom-end TQ.
An off-road y-pipe, x-pipe, or h-pipe is referring to one without catalytic converters(cats).
For emissions-compliant applications, gutted cats, high-flow cats, or stock cats may be used.
4. Exhaust - cat-back
The part of the exhaust system that goes from the mid pipe to the exhaust tip is considered the cat-back.
You can purchase bolt-on cat-back exhaust systems that require no fab work. However, in higher-HP applications, custom exhaust work is often needed.
5. Exhaust - cutout
An exhaust cutout can be installed before or after the cats and allows for an open exhaust part of the time and a closed exhaust for the rest of the time. Great for the track.
6. Cold air intake
There are many different cold air intakes out there and most of them work, but some work better than others and others are a higher quality than others.
Things to look for when buying a cold air intake are: a. enclosed filter element and b. dry filter element. An enclosed filter element ensures that you are truly getting cold air induction, not hot air induction as with an intake with an open filter element. A dry filter element is for ease of maintenance and eliminates risk of damaging the MAF sensor from over-oiling the filter element.
Volant, Outlaw, AEM Brute Force, K&N, etc. are popular choices.
7. Mass Airflow Sensor (MAF)
The only time this should have anything done to it is if you are swapping out to a Lingenfelter 100mm one. This is unnecessary for a bolt-ons only motor, only necessary on a higher-hp application. Could be used if wanted to do a true 4" custom air intake when using a 90mm TB.
8. Throttle Body
Your stock throttle body is 78mm. Unless you swap to a different intake manifold with a larger inlet, stick with the 78mm version.
9. Electric Fans
A popular upgrade is swapping to electric fans from the clutch-driven setup on the 99-04 trucks, and for good reason - not only is HP and TQ increased, but throttle response and gas mileage is also increased. The 05-06 trucks already have an electric fan setup.
Some options for an electric fans setup is adopting a set of fans from an LS1 f-body or vette or the unit from the 05-up trucks, however the newer truck unit requires the use of a 34" radiator. There is always the aftermarket option of you choose to go this route.
The fans must be controlled somehow. Either by a wiring harness hardwired to the pcm and turned on with a tune, or operated by a simple toggle switch, just dont forget to turn them on.
10. Under drive Pulleys
Under drive pulleys are simply under driving the accessory drive to reduce drag and free up HP. It is recommended when purchasing these to get the over driven alt. pulley also.
After doing some or all of these mods you may need to upgrade your fueling components.
A 255lph fuel pump is a popular upgrade.
Without any internal engine mods, some 8.1L truck fuel injectors will be plenty of fuel for your engine. They are a direct swap also.
Replacing the gears in your differential wont increase your HP or TQ but will help get you off the line better and make it feel faster. But be careful, bigger is not always better here. The higher the ratio, the better you will get off the line, but the more rpms you will turn on the highway and in turn the worse mpg you will get.
13. Limited Slip Differential (LSD)
The stock G80 locker can be a weak unit and can break under even the slightest increase in torque. Upgrade to an aftermarket LSD. The Detroit Tru-Trac and the Eaton LSD are both very nice units.
I recommend before EVER going to a dyno to get a built drive shaft. The stock piece is not meant to be driven to 130mph+ and will not stay in one piece if done so. Upgrading to 1350 u-joints or better is always nice.
15. Torque Converter
A higher stalled torque converter (stall) can be very helpful in reducing track e.t.s. However if you are going for a dyno number stay away from a stall for it will show lower dyno numbers than that same setup with a stock TC.
MODS that have proven NOT to work
1. Mass Airflow Sensor (MAF)
The Granatelli MAF is NOT worth the cost even if its free. I know of more than one occasion where they have caused multiple tuning problems. This also goes for descreening the stock piece.
2. Throttle Body Spacer
There are some vehicles that this works on but not the LSx-based trucks. It works on a vehicle where the air AND fuel flows through it but on our vehicles (MPFI) it just makes a loud whistle.
I dont know how they think this can work but it doesnt. All it is is another restriction in the air intake - NOT GOOD.
4. Spark Plug wires
This is debated but with our short wires there are little to no gains to be seen other than ohm resistance.
5. Vararam Velocity Stack
Reports of poor fitment along with little to no gains = not worthy product.
6. MSD Coils
We do not have a problem with underpowered spark plugs or wires. Our stock ignition system is fine.
Some of the above info has been compiled from different sources thruout the years and is beneficial to all. Enjoy!