Welcome! Hopefully this will clear up some details for you, I am sure others will add to it but here it goes.
RS = Base Model Cloth interior, no sunroof (unless ordered special), no power options (unless ordered special), disk brakes up front, drums in the rear, probably got 14" wheels, weighs a little less than all other eclipse models, and probably no side skirts.
GS = 1 above Base Model Cloth or Leather interior, possibly a sunroof, maybe (probably) power options, probably have 16" wheels, disks all around for brakes, and possibly have side skirts.
Other than that they are basically the same car. Same engine, same tranny's, same everything (I think) then whats listed above. Hope this helps.
