My mileage has dropped from 12-14 mpg to 10-12 mpg. I have a 2004 Silverado 2500 4x4 v8-6000 with a K&N filter in the stock airbox. I also have 285 wheels on the stock rims.

The dealer told me that every 15,000 miles I need to remove the throttle assembly and remove carbon or my mileage will decrease. They want to charge $90 to do it, and of course I'm skeptical. Has anyone heard of the requirement for this?

I'm also looking into other ways to improve my mileage. I thought about looking into maybe an airbox modification or something similar since it looks like a very bad design (basically mashed against the fender wall).

I'm passing everything except a gas station now, and with gas prices only going up... I need help. :(

My mileage has dropped from 12-14 mpg to 10-12 mpg. I have a 2004 Silverado 2500 4x4 v8-6000 with a K&N filter in the stock airbox. I also have 285 wheels on the stock rims.

The dealer told me that every 15,000 miles I need to remove the throttle assembly and remove carbon or my mileage will decrease. They want to charge $90 to do it, and of course I'm skeptical. Has anyone heard of the requirement for this?

I'm also looking into other ways to improve my mileage. I thought about looking into maybe an airbox modification or something similar since it looks like a very bad design (basically mashed against the fender wall).

I'm passing everything except a gas station now, and with gas prices only going up... I need help. :(

The TB does need periodic cleaning, but I doubt that it is causing your mileage decrease.

Did your milage drop when you put the 285's on? If you started out with the standard 3.73's, your new ratio is now around 3.50 which puts a hurt on your mileage. If your speedo hasn't been recalibrated, you are also getting more miles per tank than it appears.

I know...pretty basic and I'm sure you've thought of these, but I had to ask.

Yeah... When I put the larger tires on... It had about .2-.3 mpg difference. I didn't recalibrate my odometer, since I really didn't care about that minor difference. My problem is the 2mpg range difference (which is huge considering the percentage drop). I only have abour 20k miles on it right now. It's not like I have 100k miles on it while a grip of wear, tear, and carbon buildup.

I would also add that towing sucks hardcore. I get about 7mpg towing my trailer. :( I don't have the 4.10 ratio which I kind of regret. I looked into changing it, but it would be too expensive because of the front differential too (it's 4x4).

Yeah... When I put the larger tires on... It had about .2-.3 mpg difference. I didn't recalibrate my odometer, since I really didn't care about that minor difference. My problem is the 2mpg range difference (which is huge considering the percentage drop). I only have abour 20k miles on it right now. It's not like I have 100k miles on it while a grip of wear, tear, and carbon buildup.

I would also add that towing sucks hardcore. I get about 7mpg towing my trailer. :( I don't have the 4.10 ratio which I kind of regret. I looked into changing it, but it would be too expensive because of the front differential too (it's 4x4).

I did the same tire change on my HD, but it has 4.10's. I knew I was going with larger tires before I bought a new truck, so I picked a truck with this ratio to begin with. My ratio is now about 3.80. You'd think mileage would increase, but it stayed the same, or slightly worse. You need to calculate your change in odometer readings according to the larger diameter to accurately figure fuel milage.

My last truck started out with 3.42's and I put 285's on it. I would think twice about doing that again. Too far below the intended powerband. Killed the fuel mileage.