2005 chevy colorado won't start - sometimes

I have a 2005 colorado, 2wd, same problem. started about 2 weeks ago, won't start sometimes. i'll crank it and won't start, leave it alone
for about five minutes, try it again and again until it finally starts. when it does start, runs smoothly as if nothing happened. this happens 2-3 times a week. this tuesday, i was starting it up in the morning and same thing happened. when it finally started, the engine line was off and the whole truck was shaking. so i turned it off and turned it back on and it was ok again. so i dropped it off to the dealership, showed him the video (i used my treo phone) of it not starting. i was worried they won't be able to re-create the problem so i had it video taped. i got a call from him friday, saying they replaced the battery because it was drained (i don't believe how it could be the battery, but anyways) and they are still trying to find out why it won't start.
truck is used everyday going to work, 30 miles one way, and on long drives on some weekends. i change oil every 3,000 miles (usually comes every 2 months) using mobil1.
what should i do?? do i start asking about the fuel filter? fuel pump? what could be the possible problem? i'm a female and not too much a car/ truck enthusiast so i don't know much about these things all this is still covered by the warranty, right? it's only at 20,000 miles.
Thanks for all your help.
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My 2001 s-10 did that for a while, then I took it in under warranty, and the dealer did something, and all was well. Then it started doing it again, but only when the gas gauge read 1/4 tank or less. At this time, the warranty ran out, so I made it a point to gas up when it hit 1/2 tank. That was a couple years ago, but now it works just fine. It seemed to have cleared up after I ran out of gas on the local freeway (forgot to gas up, ran the tank dry). It had a previous problem with tail lights going out, had that fixed, too, also under warranty.
Now my only problem with it is one of the lights on the radio is out. 60,000 miles, and it's still got the original brakes and tires, all working just peachy keen.
I bought a lottery ticket that's guaranteed to win $47 million, and next Wednesday, I'm gonna cash it in and buy me a shiny new red Colorado. >;-]

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