Why am i getting smoked by 2500's?

Newbie here. Need help guys. I recently have installed on my 04 sierra z71, a cold air intake, Dynatech Racing headers with high flow cats, magnaflow dual exhaust (not true duals)and installed the Diablo performance tune. I always use the highest grade gas from the same company everytime. Twice i have been outran by sierra 2500's and it's bothering me! One was a 2007-2008 and just this past Sunday, a 2004-2006 2500 4x4 which the driver says was stock. What gives? Am i not getting the most out that Diablo tuner or are the 2500's just quicker? Help!!  

first off, your cold air intake is barely a performance mod, your Dynatech headers - are they longtubes, midlengths, or shorties? Longtubes would be the best, but if you've got bigger primaries, you're losing all of your low-end torque, midlengths are also good, but without proper tuning, you're not really helping yourself, your computer doesn't know that anythings done and you're still under the stock vehicle parameters, your "highest grade gas" isn't helping either, again, your computer isn't tuned for it, so you're wasting a few extra bucks every fill-up

you should also know that the Diablo isn't doing a whole lot for you, a cookie cutter tune isn't for everyone, especially if you're spending money on headers and the like, shoot for a real tune, such as www.blackbearperformance.com or Nelson Racing (google it) or even Wheatley Perfomance (google them also)


long story short, your 4.8 or 5.3 (since you didn't specify) makes power at a higher rpm than the 6.0s or 8.1s, not to mention that they make more power right out of the bag than you, and your headers moved your powerband up, taking away more of your low end

unless you were racing diesels, then disregard all I've said and plan on losing every time, no matter what  
2003 Chevy Silverado

you have a 4.8/5.3/6.0? you need: cold air intake, exhaust system and a tune, see my posts for more details!

How much more do the 2500's weigh compared to your truck?  I know they are heavier, but like h20son said, they make alot more power right out of the box.  Unless their weight totally negates their extra hp, or your mods are really giving you a nice gain you could still be at a power/weight disadvantage.  

The other thing to look at is gearing.  Being heavier duty for towing, the 2500 might have better gearing than yours (although I'm pretty sure they have similar options available).

What motor is in your Sierra?  

What speed are you getting smoked at? Are the 2500's diesel,if so once moving the diesels are quicker than people think especially if they're hopped up. A good friend of mine has a 1500 truck with a hemi and couldnt believe he couldn't keep up with a 2500 with a cummings diesel.  

prob a 4.3 with 3.0 gears...makes a HUGE difference in the gearing