loss of performance

I have a 2002 silverado extended cab 2wd 5.3 auto with 3.73 gears. This truck has 84,000 miles and use to be very fast 15.62 @ 92 mph in the quarter on my g-tech.when it was new. I raced my buddy with a 2000 4wd just like mine and could barely beat him by a truck length. I put my g-tech back in yesterday and it only ran 16.64 @ 85 mph I have changed the air, and fuel filter but that has not helped.
Does anyone have any suggestions or advice? It would be greatly appreciated. The truck is bone stock

could be normal engine wear, or it may just need a tune-up or new plugsor something.. slick 50 or something along those lines wouldn't hurt either.. average life span for an engine is around 150k or so... they wear out eventually. If you can afford it, spring for a rebuild.