I have a 2000 5 speed and i feel that I keep my foot out of it fairly well but i usually only get about 15 mpg. I have 373 gears and I usually start in second unless i'm on a hill. I know this combonation doesn't help but i didn't think that it would put my mpg's at 15 when i feel i should be getting around 20. I just recently changed my fuel filter so I know that isn't the problem and i don't have a fuel leak. I'm a little stumped as to why it is so low. Any help would be greatly appreciated.

 

Try cleaning the MAP and IAT sensors and check your air filter. I just noticed this thread further down the page. https://www.dieseltruckresource.com/...r-t299245.html

 

.........Get ur valves adjusted........kim......

 

Where did you get 3.73 gears for a 2000?

 

i think he means 3.55 gears

 

Sorry to high jack the thread, noticed a decent drop on mine as well, have a 99 2500 24valve qaud cab long bed. Cleaned the iat and map, air filter looks good, everything is stock, tires are 265/75/r16. gears i wanna say are 3.55's. when i got it was really low around 13.4? then it went up to 17.5 on freeway and has dropped to 14.7 mpg's no matter where i am. Guy I bought it from said he just had a fuel filter an oil change done. I did the apps reset and I think that may have caused they change..

 

ya my truck is the same way, i get 14 in the winter and 15 in the summer...

 

Lift pump pressure could be low makes a big differance when is at 16lbs+

 

It could just simply be winter fuel,you will never get the same milage on winter fuel as you with a summer blend.

 

ya thats what i was thinking, plus i also read that your timing is different acording to intake temps... so that could also explain the change...

 

tire pressure , alignment, tire style, winter fuel, heavy left foot, vp failing, headwind, load, brakes dragging, valves out of adjustment, operating temps, road surface.........

The list for possible causes can go on and on.

I usually look back at anything that has changed recently or if I have done anything to my truck that may affect mileage.

You didn't mention what the majority of your driving style is city/town or highway.