they need the air flow. 90% of the climate out there, you probably could get away with less but in the SW, you need all the cooling stack you can get. The loads these trucks are rated too are no joke and trying to pull that same load out here in the heat will tax a cooling system fast. remember, we are talking HP that is 150hp over a LB7 at the crank. make any lb7,lly,lbz or lmm make 450 crank hp, tow 25-28k out here in the summer and still keep every fluid in check as well as egt's while you flat foot it up a grade is a hell of a challenge. ive seen healthy 100% stock LMM and LBZ trucks get hot pulling our grades and their cooling system was tip top. GM did alot of testing out here. every MFG did during the summer. 115* out side air temp with roads radiating 160* air into the front air dam makes cooling a bitch to do when you are using that air to cool it.