Got me a new truck with a slant Six, what should I do?

If you want a little more performance out of that little 6 just put a stock 2bbl manifold on it , skip the header and 4bbl carb, there's not enough gain for dollars spent on that stuff. It looks like it already has a larger exhaust on it already, a 2 1/4" - 2 1/2" pipe gives the best performance over stock. Give it a good tune up or just make sure everything is in good working order and cruise on down the road with it. You should be able to get about 20 MPG out of that truck if it's got the overdrive 4 speed.