I recently took a 450 mile round trip to my cabin towing about 2,500 lbs. Before I left I was averaging approximately 13 mpg. Since I've been back, I've seen a decrease to approximately 10 mpg. I've filled up twice and it stays between 9.5-11. Does anyone have any idea what would cause this decrease?

 

Check your intercooler clamps, could be a boost leak.

Need more info.

 

Thanks. I'll check that.

What kind of additional info is needed?

 

How many miles are on your air filter and fuel filter?

How many miles on the truck?

 

The truck is basically brand new and I know that the mileage should go up with time, but mine seems to be going the opposite. I also thought that towing would speed up the process, but that doesn't seem the case.

It has approximately 3,800 miles and was in for its first oil change at 3,050 miles. The air filter has about 1,200 miles on it.

 

My first tank was 14 MPG,now on third tank and it has gone down to 11 MPG,pretty sure it is because my wife has been driving it,she is all over the place with the throttle pedal,it is like being on a roller coaster when riding with her.
You may want to try towing something,that has always worked for me in the passed.

 

I have towed a few times before. It hasn't been much - between 1,500 to 4,000 lbs. Like I stated in my original post, I noticed the decrease after returning from a 450 mile round trip towing 2,500 lbs.

 

When did you put the 20" wheels and tires on and did you have the speedometer recalibrated? If the tires are taller than stock you will register less miles on odometer, it will also effectivly change your gear ratio and make the engine work harder when towing thus using more fuel.

 

The wheels and tires were on the truck when I was averaging 13 mpg and my mpg calculations have all been done by hand. So, basically, everything was the same on the truck before and after the trip I took. Before the trip I was averaging 13 mpg and for the past three tanks of gas, I'm averaging 9.5-11.

 

Go ahead and change the fuel filter. You may have gotten some bad fuel.

 

I changed the fuel and air filter, did an oil change and aired up the tires a bit. 14000 miles on her. The air and fuel filters were both filthy. I have seen a roughly 2 mpg increase going by the computer since the change which puts me back to the mileage I was getting when it was brand new. Roughly low to mid 16's in town.