Yes, you can go to Autozone and see if they can pull a code for you. If they can retrieve one, please come back here and let us know. That will give us a lot to work with in helping you out.
While there, I would go ahead and grab for quarts of ATF (Dexron III/Mercon) and perform a drain and fill. A flush my not be the best thing in the world for you. You can read why
here.
As for the drian and fill... Grab a 3/8" drive rachet and remove the plug from the bottom of the transmission. Let the fluid pour out. Once it stops, reinsert the plug and add 3.5 quarts through the dipstick tube. Start the vehicle and work it through all the gears, while holding your foot on the brake. Leave the engine running and check your fluid level and add as nessecary to top of the level.
