Does the 03 suburban have a cabin air filter? How do I get to it and change it. The 03 1500 4wd doesn't have that little door you swing down under the glove box. Please help!

No you do not have them. The cabin filter was deleted in ALL of the 2003 Chevrolet trucks.
If you want your cabin air filtered it is a simple taks to install a set of filters in your truck.
Let me know if you want more info on the retro fit.