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Hello, new to the forum. Just picked up a 2003 2500HD CC SB 4x4 w/allison and 120k miles (all stock, well maintained, know previous owner). It is not a daily driver and will be used primarily to haul my 24' enclosed car hauler (flat front, barn door aerodynimics!) .

My dad just towed the trailer (no car, but about 800lb of tools and gear -around 4800lb) to Phoenix from Calgary. First the fuel economy averaged 10-11mpg at 75mph. I thought it would be better as my 5.3L 1500 Sierra got 8 mpg at 70mph in Drive/3 gear with the trailer loaded up (~9000lbs). Will a cat back exhaust or programer help with mpg while towing? Are there any cat backs that retain stock noise levels in the cab? What is a good choice for a programmer for small hp gains, increase mpg and stock relability?

Second on the long hills the engine seemed to "loose" power as the hills went on. Speed would drop to 60mph, engine temp increased slightly and the engine fan roared, trans temp remained constant. Is this normal, why does it happen and what can be done to eliminate it? I always hear guys brag about towing their 12000lb 5th wheels up steep/long hills at 75mph with duramaxs.


Thanks
 

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Second on the long hills the engine seemed to "loose" power as the hills went on. Speed would drop to 60mph, engine temp increased slightly and the engine fan roared, trans temp remained constant. Is this normal, why does it happen and what can be done to eliminate it?

Thanks
It is an unfortunate reality of forced induction power. The intake air heats up and that creates a lot of added turbo compression heat, less dense air charge, lots of pressure drop, and all that extra heat is shed by the intercooler right into the fan clutch. The fan uses a lot of power when it runs also, so the trick is to keep the fan off.

But there is a lot that can be done about it, starting with a properly designed cold air intake. Read more about what happens HERE My fan has not come on in a year now.
 

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Hey welcome to the site!

The motor itself is a big motor. Mine unloaded gets 13 around town. I just towed 10,000 this weekend and it averaged 10mpg. So regularly your gonna use more fuel than your 5.3. Any exhaust will help especially if you loose your catalitic converter, I used a 4inch MBRP with mine then eliminated the muffler. When I towed the 10k it haule fine with no drown at all. The programmers are all more or less the same. I like hypertech because of the cost and design. Make sure if you get a programmer not to add over 85hp or you'll risk burning the tranny.

With towing, everyone drives different . I baby mine and dont mash the throttle to the floor when going up hills to get more power. If your like me then you will loose power but if you dont care and go like hell you'll tear ass up the hill but burn the tranny and turbo or motor in a few thousand miles.



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I'm not sure here but doesn't the Duramax monitor EGTs and then defuel accordingly? I could easily be wrong because I have an old 12 valve Cummins, but if it is the case you might look into a turbo back exhaust. That should drop your EGTs at least 200 degrees and help with the defueling. A turbo back system will also free up some horsepower and your turbo should spool faster. You might want to look into an exhaust system anyway if you are adding more fuel with a programmer. I personally like Silverline exhaust systems because they are all stainless and sound really good, but there are a lot of really good exhaust systems out there.
 

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I stand corrected, maybe I was thinking about some of the aftermarket chips. Lower EGTs are still a good idea.
 

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Basically if its going to be a designated towing rig you need to put a cold air intake on it, a mild power aditive, and a good open exhaust, she will handle the hills alot better and will get better mileage.
 
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