Truck burning excessive gas. I replaced crank shaft sensor, did not improve mileage

no
the purpose of the crank position sensor is to tell the ECM where the piston is so that the ignition can fire the coil and to the plug at the correct time
if it is defective , it will not allow it to fire , , run properly
code p 0018 refers to crank shaft /cam shaft position , bank 2 sensor A --correlation===causes wiring-- Crank sensor--- Cam sensor-- mechanical fault

when you see mechanical fault and you have a sluggish engine or other problems , it could be that the cam control servo is malfunctioning and that is reporting as a correlation problem because the ECM is getting varying readings as to where the cam position really is in relation to the crank position and rpm

A bad pump sometime for a fast diagnosis get somebody to crank the engine and you take a hammer a knock on the gas tank 90 percent of the time the electric pump will start your truck its not a fix its a simple way to see that the gas pump is the problem change it

Replace air filter.

Driving habits are the main reason for bad mileage including: excessive idling, fast starts and stops, fast driving in general...best speeds are 50 to 60 MPH for economy, city driving uses most gas,
Mechanical problems include underinflated tires, leaving windows open at highway speeds, not keeping engine tuned up, not changing lubricants at proper intervals, not greasing wheel bearings, not aligning and balancing tires..etc

Sounds like you have a timing issue with the truck. Could be your ecu or the sensor(s) that feed data to your ECU.

wont help but taking that cat off will also if your running rich truck needs less fuel more air check air filter....cutting that catylitic off depends on where u are check the law.....but that will improve mileage alot ...so would dual exhaust....BTW all the O2 sensor does is tell u when its out of wack so cant see it being the problem if no engine light warnings...

Driving habits...incorrect tire pressure...excessive weight in car...low oil/old oil. Many things affect mileage. My 2002 max needed a new O2 sensor. Once replaced the mileage improved slightly.

this is the first sign that your oxygen sensor is shot replace it and you will see the fuel mileage come back.

check your thermostat and the engine cooant sensor.

it could also be the oil pan gasket, or the manifold gasket. if it's the manifold gasket, when you remove the manifold to replace it, take the time to clean out the mixing chamber. it'll be filled with gunk and cleaning will improve gas mileage.