It's impossible to say with any degree of certainty. You can't measure the drag coefficient of an object by looking at it. Try it; what are the drag coefficients of these trucks?
...versus this:
...versus this:
...without seeing Chrysler's own numbers. Go ahead, take a guess.
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The answers are (select to show text or click link for source): #1)
Cd .42; 2)
Cd .399; 3)
Cd .36.
Chevrolet has never published drag numbers for the Silverado, so the only way you're going to answer your question is to track down an engineer who worked there and is willing to divulge that information. Good luck!