Bad Fuel Mileage Suddenly

[buckshot]

Hello all,

 

I have a 2000 2500 regular duty with a 6.0 and 3.73 gears and 285 75 16 AT tires. I used to get on average 16 mpg and now it has just dropped to 12 mpg. I changed fuel filter, air filter, fuel pump, fuel pressure regulator, tps, crank position senser, iac valve. I still use the same fuel I always have regular octane fuel. Also my tranny has not been wanting to shift from 3rd to overdrive. It is reving all the way up to 26 hundred rpms before shifting. I have had in the past a tcc code pop up on my scanner but it went away and then came back and then went away. Any help would be greatly appreciated

[jrtrip]

Hello all,

 

I have a 2000 2500 regular duty with a 6.0 and 3.73 gears and 285 75 16 AT tires. I used to get on average 16 mpg and now it has just dropped to 12 mpg. I changed fuel filter, air filter, fuel pump, fuel pressure regulator, tps, crank position senser, iac valve. I still use the same fuel I always have regular octane fuel. Also my tranny has not been wanting to shift from 3rd to overdrive. It is reving all the way up to 26 hundred rpms before shifting. I have had in the past a tcc code pop up on my scanner but it went away and then came back and then went away. Any help would be greatly appreciated

 

Did you check to see if your MAF is dirty?

[HyperBuzzin]

I had a similar experiance. It was the O2 sensors (I think they went bad due to cat being gutted by the previous owner). But they would bring up the SES light. I'd get it reset, it'd come back on.

Changed the cat & sensors (after changing a sh!t load of other stuff first) and all is back to normal.

[TonyMazz]

...well based on the post, the first place to check is the tranny...not going into overdrive is an issue. Based on the fact that it's a 2000 with a probably a boat load of miles, I'd have the tranny reviewed. Whens the last time it was flushed, cleaned?

 

Not going into over drive will kill you mileage....

 

let us in on how many miles are on the truck, when's the last time you did a tune up (plugs, etc)....?

[wdidn]

...well based on the post, the first place to check is the tranny...not going into overdrive is an issue. Based on the fact that it's a 2000 with a probably a boat load of miles, I'd have the tranny reviewed. Whens the last time it was flushed, cleaned?

 

Not going into over drive will kill you mileage....

 

let us in on how many miles are on the truck, when's the last time you did a tune up (plugs, etc)....?

 

I suggest changing the filter and fluid to start with.