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.