Okay Guys, I know somebody here can answer this question even though my Chevy dealership can't. I have a Z71 Vortec 5300, gas mileage rated at 15/18. I want to trade for a 3/4 ton Vortec 6000. How much am I going to be hurt by fuel economy? Since the government does't require fuel ratings to be posted for these, nobody seems to know what kind of mileage they get (or maybe they don't want to say). Thanks.