Bad mpg

[Bigmanj101]

I have a 1991 MM and I get horrible gas mileage it's a auto , but it still shouldn't be this bad anybody else have this problem or know what to fix , I've done checked everything

[camoit]

Welcome to the site.
How long have you had the truck?
What size it the engine?
Does it idle OK?
What kind of MPG are you getting now?
Fuel injection or carb?
And the big one have you ever changed the timing belts?