I have searched all day for info

[Leedogg]

on 1987 3500 crew cab duallies. I found one with the 454 and th400 and was wanting to get some specs on these trucks. I finally found a site with hp and tq ratings...but as far as payload, towing, fuel ecomomy. I know the motors back then were anemic...but my old 92 350TBI got great mileage...wonder if the 454 would be at least reasonable(especially if i do a 4l80/85 swap later. I would hope 11-13mpg stock...is that even close?

Any info or links to good info would be greatly appreciated!