Does anyone know what size speakers are installed in a 2003 GMC Sierra 1500?

[Heckbo]

I am looking to upgrade the stock audio system and would like to know what size speakers are installed before I go and buy new speakers.

 

[RacingFan]

I am looking to upgrade the stock audio system and would like to know what size speakers are installed before I go and buy new speakers.

I have a '97 extended cab so I am not sure if they are exactly the same, but I have 6-1/2" in the door, 2" tweeter built in the door handle, and 4"x6" in the rear pillar. I haven't seen other trucks with the 2" tweeter so I am not sure if that's a factory upgrade or what. I have only had the truck for a couple months.
You can probably go to something like Crutchfield and use their 'Outfit my car' function to confirm if yours are the same.
Good luck!