If you change the exhaust make sure you size it properly.
Autolounge.net | Calculators | Exhaust Pipe Sizing
Your biggest drag is going to be the underside of a pickup truck, I'm not sure if chevy changed the underside of the s-10 when they built them as an electric vehicle, but it would be worth looking in to.
I know that one draw back of the S-10 is that they are heavy for a small truck, compared to a Toyota pickup truck of the size is 10% lighter.