Well seems like everyone has good answers to your question but here's an easy way to find out which one is right if your buddy is getting 19 pulling that trailer he's probably just getting lucky on average these 12v motors will get anywhere from 10 to 16 loaded 19 to 25 empty fold your mirrors in cardboard the radiator and do 55 you can even get upwards of 30 its all a matter of wind resistence pulling a cargo trailer with a flat front is like pulling a brick wall the truck don't care if it wieghs 100 pounds or 10000 pounds the trans might but the engine won't. Try servicing the trans make sure the bands are tight and then see what you get it may or may not help also put your camper shell back on for the long trips that will put the air over the trailer instead of right into the nose of it if that doesn't help you might have an engine problem if it has an egr valve there's a good place to start also the cat may be clogged and as much as I hate to say it for those of you who like your ac as much as I do turn it off

 

All good reasoons, heres another one, how often do you change your fuels filter?, and clean the pre filter?. Fuel millage can be affected by dirty gear oil in the diffs, and heavy weight oil in the engine. you also mentioned you had a fuel plate, maybe your buddies plate is more conservative, or better tuned. Just keep in minde, if you have a well maintained truck it will better perform. FRICTION IS THE ENEMY

 

go with the tallest skinniest tire you can get thatll help you

 

Taller tires as we all know decrease rpms yes but in return the trans has to work harder to roll them so you may gain mpgs but you lose the trans faster. The other thing is that taller tires make it harder to pull a trailer the trailer sits un level making the rolling resistence higher and causing the tires to wear faster also it allows turbulant air under the trailer wich increases drag wich decreases mpgs so yeah you choose

 

Driving habits can be a huge factor, too... If you see a solid stream of black smoke behind you everytime you accelerate from a red light and such... well... there's y'ur problem.

Anyway, I get about 500 miles per tank from a full gauge to a 1/8th gauge.... I have no clue what that comes out to in mpg. Think the tank is 28gallons, but not even sure about that... Also, don't know how accurate that odmeter is. The aftermarket tires I have on it made the truck sit about a inch or two higher. With the stock tires I was getting about 515 miles per tank. But I imagine that's due to the difference in odometer readings, between the difference in tire height. I'm probably still getting 515 per tank.

I wonder if the lack of sulfer in todays diesel, has anything to do with anything....
Speaking of which... does anyone use sulfer additives? I haven't, but my dad says I should...

 

Yes, lack of sulffer does effect these engines. I try to add some lube additive to mine with every fill up. Even if it doesn't help my MPG's, I feel better knowing I am getting sufficient lubrication to my fuel system.

 

I spend the 30 bucks on a gallon of lucas everytime I fill up keeps my fuel system clean and provides plenty of lube for it all a gallon may treat 300 gallons but I use it all for 35 gals wich is what the tank is in our trucks but to each they're own

 

Wow, i wish i had your money, as much as i drive if i added a 30 dollar gallon of lucas, i could by a new fuel system every month or so. I just use a bottle of diesel clean every other tank or so.

 

The company I work for pays for my fuel so its on they're dollar not mine I easily got through a tank and a half a week and never get fuel from the same place so its importants to have some additives in there to stabalize the fuel

 

Sometimes too much isn't always good. But that is my opinion.