I'm glad you figured out your problem!

 

I never leave nothing stock either. I'm running 37s with 46psi and 9 inches of lift in truck and it gets a hand calculated 19 on highway and 15 in city. I'm running 4.10s though and what I believe is the only way to keep the mileage up is to lower the speed. Iv'e seen a 5 mpg difference from 60mph average to about 78mph average. These trucks are already pretty tall and when you go adding half a foot of lift not to mention an incredibly wide and heavy tire into the equation your gonna have problems.

 

I pulled a 24 foot camper to wisconsin and back when the truck only had between 1 and 2 thousand miles on it. I drove 75 with a few shots up to 80. I only got around 9 mpg. The camper weighed around 5000 pounds. Now with 7500 miles on the clock it all of a sudden jumped up tramendisly. A week ago I pulled a 873 Bobcat on a equipment trailer 60 miles round trip at 65 mph. I was told the skid loader was around 8000 pounds and the trailer around 2000 or so. I got in the mid 11s buy the overhead wich I have found to be real accurate. Now last night I pulled a 7 series bobcat the same rout at the same speed and it never dropped below 14.5 the hole way. I figure I still had to be around 8000+ pounds. I hope I just hit the majic spot where the milage goes up. Just hang in there, I does apear that there may be some truth to the milage jumping all at once. I want to go find something real heavy and pull it to se what happens.

 

I drove my boat to 400 miles today. This was through very hilly country (Page, AZ to SLC, UT). The mileage fluctuated a lot. On the way down, empty, I was getting about 14-15 mpg. On the way back, about 8-9. But, again, we are talking about miles up 6% grades. My boat is about 7000 lbs dry, not counting half a tank of fuel, 20 gallons of water, gear etc. I would not be surprised if she was 8000-8300 lbs today.

Most of this was 60-70 mph, depending on traffic and road conditions. However, some of it was 35 mph uphill.

Still, I was pretty happy. Considering the truck never struggled and I just came from a gasser, it worked well. The truck went from 500 miles on Thursday to 1500 today...

Hope to see improvements, but even if they aren't great, it's still much much better than the 5.4L Ford engine I had. It would suck the gas and still couldn't pull..

 

I've read all of these posts and still can believe your gas mileage is that low. You seem to have an understanding of all of the factors that can or cannot make a differeance. Yes, 37" mudders will make a differance as well as a lift and lights and so on and so on.....but your trailer is not that big nor heavy. I believe there is something more seriously wrong than the obvious. Just for referance, I have 3" Lift, brush gaurd with lights, 10,000 lbs winch, EZ Edge, 4" Exhaust and AFE P7 and run 10-12.5 (hand calculated) MPG with a 10' Camper @ 3900 lbs. and a boat @ 7200 lbs. throughtout Western Washington in a mix of hills, flats and stop and go driving. 22 MPG everyday unloaded. Not trying to rub it in, just comparing.

 

Those numbers are kinda hard to believe,with all due respect.Im running nearly the same truck with 48re and 3.73's andwith an egg under my foot im seeing average of 15 mpg.I also run high tire air pressures and use Stanadyne additive to boot.Truck has about 19k on the clock.What gives?

 

Just got back from a 2 week 3100 mile trip. Southern California up the Interstate 5 all the way to Portland, Or. Took the 30 along the Columbia River to Astoria. then down the 101 back home. Very hilly, and windy. Pulled a 28' travel trailer with my new (3000 miles on it at the start of the trip) 04.5 600 with 4.10 and 48re auto trans. Conservative weight figure on the trailer is 7,000 lbs. My buddy has a 2002 Ford with gas 5.4 and is pulling a much lighter 22' trailer. Maybe 4500 lbs. He averaged about 10.5 to 11 mpg which I thought was GREAT. He has a smaller tank so he needed to fill up more often, but most fillups he would put in 21-22 Gallons and I would put in 15-16. My average MPG was 13-14. We drove at about 60 MPH most of the time, except when we hit some huge grades my buddies Ford would slow down to say 40-45. At first I was playing with him. I would pull next to him, wave at him, and then GAS IT! Adios amigos. Back to 60 in a flash! Slow back down and get behind him, and repeat. Almost like I didn't even have a trailer behind me. On some 8% grades I admit my truck shifted out of overdrive, but no problem keeping speed. Weird sometimes is that as I was cresting a BIG hill it would downshift out of overdrive, and then just as quick shift back.

All in all I think the Cummins was SPECTACULAR! My wife even enjoined splitting the drive time, which she hated doing with the old truck (1995 Dodge with 5.9 360 gas).

 

Are you running gauges? If so EGT numbers please.

 

my 04.0 (555ft-lb) has 12,500miles, almost 5000 of that towing 10,000#.
I'm all stock.
I see 12 to 14 mpg hand calculated
I don't drive much over 68mph

 

Perhaps I wasn't clear in my message, I was getting 14-15 miles per gallon on the way down (empty). I was doing 60-70 on the way down. On the way back, hauling the boat, I was getting 8-9 mpg.

I don't find that hard to believe, but my message may have not made it clear.

 

No, everything is completely stock. Why are you asking about the EGT numbers?

Thanks

Brian

 

Sorry,i transposed posts,i was refering to "AllTork" getting 19 mpg with his set up,a few posts above yours.

 

Just curious i 'spose, what year is your truck?

 

2004.5 Cummins 600 Quadcab 2500 4x4 4.10 gears, 325hp, tow group, Laramie, Prem Leather power seats, auto trans, Rear slider, Fog lamps, Body side molding, Infinity system, Arma Coating spray in-liner, Nasta SS Nerf Bars, Dodge mud flaps and rear wheel liner, Graphite w/ silver 2-tone.

That describes it completely!

 

Thanks.I thought i had heard/read the 600's were running hotter egt wise than the previous motors,if so i would highly recommend gauges especially if towing.Matter of fact,i wouldnt tow anything moderate or heavy without them.Just my .02 Mark.