You must understand concepts to be able to score well in GC on the DAT.
understand delta G,H,S and be able to know what they are in a given circumstance.
Understand rates and Le chat's principle.
understand Ksp and the solubility rules
understand redox rxns and how to balance them.
understand phase changes and what happens, what are the names, what are the delta g,h,s in each change
etc etc.
you must go through the destroyer and be able to do every single problem in the GC section, do it 4 or 5 times.
i got my GC from a 16 to a 20 by doing destroyer + kaplan blue book. no joke. it's really not that hard on the real thing.