Performance parts do not actually increase the HP of a Durango. They are anti-gravity devices that actually reduce the weight of the vehicle in order to give the appearance of an increase in power.
Headers and catbacks - since the engine is probably the heaviest part of the vehicle the headers support if from beneath and the anti-gravity starts to allow the engine to rise. The catbacks extend the length of the vehicle and in a similar matter keep the rest of the vehicle level with the engine.
PCM - connects to the wiring harness and makes all the wires pull evenly across the entire vehicle, thus maintaining an even lift of the vehicle.
Throttle body - again since the engine is the heaviest item the TB is centered basically in the middle of the engine providing a gentle lift to support it.
Tony's Air Intake - as air passes through the K&N Filter it get's saturated with anti-gravity matter that passes through the engine again making it lighter.
As each of these devices are connected to the Durango they slowly reduce the overall weight. The initial weight is around 4600 pounds. After the installing the Gibson headers and catback the weight was reduced to around 4020 pounds. Tony D's Intake shaved about 300 pounds off and the TB took another 850 pounds off. There is a lot of copper wire in the Durango and the PCM really does the job well, the effective weight reduction approaches 1500 pounds. This brings the weight to around 1370 pounds. Now this is pretty light with the standard engines that are put into the Durango's. This causes adverse affects like the inability to get adequate traction causing a the tires to emit a loud screeching sound on occasion. This sound can sometimes be drowned out by the Roaring Fan syndrome on most Durango's. The rumble of the headers and catback are to give others the impression that your D is a much heavier vehicle.
One thing to be careful of - too many "performance parts" and your "D" may be the first "D" on the moon!
The weights may vary depending on which components you install in your Durango.