My 91 truck is one of those light duty K2500s, AKA a K1500 with the semi float 14 bolt 9.5” axle. Right now it is 99% stock, but I am going to try to turn it into a light duty off-roader but retain good on-road manners. I am also going to try to make it get better mileage, right now my 2001 8.1L big block out does it on the highway. My truck came with EGR, but it doesn’t work right now.
Most off-road trucks have those big steel welded bumpers, but they are way too heavy for what I am doing. I was considering repurposing an old semi-truck aluminum bumper, except shaping the front end more for aerodynamics. That was why I wondered if you were starting with an aluminum one. Plastic will probably be better for your on road application.
I have wondered in the past about making an adjustable air splitter, where you can keep it at a normal height for typical use, but be able to drop it down for when you need better handling due to more down force.
If you haven’t already, check out Aerohead’s photo album on pickup trucks. Especially look at the salt flats GMC Sonoma. It is designed for low drag and low lift.
Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - aerohead's Album: Pickup images