Nuther Update
Mixed Results...........
I filled until the level of fuel stayed just a couple of inches below the cap. I then ran the truck through the mountains of CO, most of the time between the elevations of 7500 ft. above sealevel and 11,500 fas. Speed varied between 65 and 85 most of the time, with one burst to 110 (side Q....how is it that we don't get shut down at 97 mph like most other vehicles?)
Total load besides a near full tank was 400 #s.
Tire pressures are still on the high side.

Todays observations....
Power is indeed massive with the box full on, BUT the "stumble" or "lurch" is very noticeable and quite annoying, so for much of the time, I had the box set near midway. I am thinking the altitude really agravates the problem.
Coming over Vail pass (roughly 11,000 fas, I was running at 80, and noticed for the first time, ALOT of black smoke. I have to wonder how the cat likes this! I immediately twisted the **** to off, and the smoke went away.
Remember that I filled the tank to near overflow, but I was very pleased to see that the needle did not center over the 3/4 line till 205-210 miles. I know gauges vary, but that was making me feel pretty darn good.
I ran much of the balance of the trip with the **** at somewhere between off and 1/2 on.
I filled up at a different pump, and while the fuel level ended up just slightly lower in the neck, the truck was definately tilted AWAY from the pump, so I am guessing this at least compensated for the slightly lower level in the filler neck. Not real proud of the procedure here, as that could make a difference of a gallon more being added, and that is very substantial when you are only checking a trip of 263 miles, but the numbers came out as follows:
263 miles, 14.48 gal. = 18.163 mpg. nothing earth shaking, and in light of the limited use of the box, I will label my efforts as inconclusive.
I will be talking with the box builder, but my gut feeling is this:
The altitude I run in is really complicating the issue. Mine is a rather unique situation, and I am eager to see what difference running down in the flatlands makes. While I openly admit that I lack badly in diesel knowledge, I have to think that the black smoke that was the result of twisting the **** too far near the summit of Vail pass and getting on it, is the result of insufficient Oxygen Make sense? Imput welcome.

 

Nuther Update......

Been a long time since I wrote on this issue, but thought I would bring it up to date.
My quadcab now has nearly 23,000 miles on it, and we recently returned from a 4200 mile trip. The fueling box acted up just prior to when we left (posssibly aggravated by my programming in some additional security keys!!), and it was back to TS for reprogramming, so it was out of the loop for this trip. At least this way, I was not able to influence the mileage with it. We were not towing, had about 1,000 total added wt. and I was running pretty fast (the highest I saw was 108mph) The 600 ran terrific, and averaged 17-18mpg, with the best tanks getting just under 19 (which required that I run more around 70...hard to do when the truck is so strong).
I don't think I ever mentioned the brand of box. It is the Ramifier by TS. They tell me it adds timing, duration, and bumps the pressure slightly. It came with a potentiometer, which is a great feature, as it allows instant adjustment. The people are wonderful, with terrific support. I do run a pyro, and temps are an issue when towing on the mountains, but you just back off some or hit the tow/haul button.
One Happy Camper.

 

Haulin,

What MPG were youy doing loaded/emt without the box?

I'm doing 13 MPG +/- emt and a stellar 6 MPG with my camper. 33k miles and according to the boy engineers at Cummins a "good nominal engine".

 

royalnine,

You have a PM.

 

wind resistance affects mileage more than weight

 

Yes. I am well aware of this but at the time I was hopeing for a little more. I have sence pulled more with it and it still leaves me wishing it got a little better. My one major gripe is that the one trailer I pull most is tiny, like I could use a small front wheel drive car to pull it small, and it still drops the milage down to around 12-14 at 55-60 mph. It is a small 6x10 flatbed with no sides and only 2 quads on it. I dont think that the truck should even know its there and it dont power and drivability wise but it shure pulls the milage down to unacceptible levels. Now I realize that the ATVs have some wind drag but not that much considering that they are sitting down low behind the truck. The trailer is so small that I use it as a yard cart behind the Grizzly for yard work. There is no real weight to speak of and wind drag has to be minnimal. I have come to the conclusion that there is a switch on the hitch that automaticly sets the fuel milage to a preset 10-12 mpg no matter what the load. I had 16000 pounds behind it at 60 and it got 10mpg. I put my little trailer and 2 ATVs on it at 60 and it is only 2 mpg better .