be carefull with this mod can cause major destruction from over heating espesially on the lly which alreadry has an overheating issue. if you read the bottom of some of the kits they say not recomended for vehicles that haul hevy loads uuhhh ? (duramax) and vehicles that are run at higher horsepower levels for extended periods of time. once again the duramax. whould stick with your stock fan works just fine.
p.s. if your lly overheats and is under waranty gm has a fix, new air box air deflectors etc. the air box is cool its the donaldson box off a lbz.