What the deal with the gas mileage?

[k72516]

There was a thread back there that asked what you guys were getting for mileage. I don't get how a 305 was getting worse mileage than a 350. It sort of worried me because I was hoping to be getting at least 15MPG all around when I buy my truck. I was thinking of getting a 305 shortbed, or blazer. I thought I would be able to do it with one of those vehicles, but I guess not? I know since I want a carburated engine that's gonna be a challenge, but I figured ya know, it's a shortbed... even with all the extra weight from 4WD... it can be made into a fairly light truck.

Any opinions or thoughts here?