Does any one out there know who is making a turbo back exhaust for the 4500
crew cab? My mileage is 4.5 miles per gallon towing, at 70 mph on the intersate.
Lly motor, 4.44 ratio, automatic trans. Any help would great.

What weight are you towing - I get much better that that towing, up to the legal max. I have found that travelling at 65 mph get much better mileage.

Mylash

Depending on how many miles you have on that LLY, you will find that it will improve somewhat, over the first 70-80K miles. With a 4.44, you are in the torque sweet spot up to 67MPH, which is why Mylash has seen better fuel mileage at 65, and weight is a real issue, when operating above the sweet spot.

You can get get with the GMC Commercial parts dealer and get the brackets for a vertical exhaust system from the 6500-8500. With a new 5" muffler and pipe, you could probably improve your mileage somewhat, but I would not expect miracles. A taller differential ratio (Code 092: 4.30:1(Requires diesel engines and GL4 rear axle (11,000 lbs.))) might be the only way to really improve the consumption at 70.

As with Mylash, I've been able to keep consumption to 9-10 Mpg at just under max GCW, by keeping it in the sweet spot (around 65Mph), using the cruise control, and timing my shifts (ZF-6 Speed) on hilly terrains. 4.5 Mpg is what we get with the 8.1 gasser, at top of GCWR and 70, so I don't know what else is going on with your rig.

Thanks for the replies. I used a Cat Scale on the total of both the versa hauler and trailer it was 23650 lbs. I just used a Bully Dog Power Pup on the 85 hp setting and it got the mileage up to 7.5 mpg @ 70 on the interstate towing. You have got to watch your egt close. I was hoping that someone made a bigger exhaust. B/D makes a 4"
brake already.
Thanks again

I am planning to do something with the exhaust, once the weather allows me to crawl around under my truck.. I am not comfortable getting cold or wet, so I can't do this at this time. I am not happy with the smell of the exhaust at advanced idle - diesel trucks should smell like diesel, not some old GM gasser mixed with paint, so if I can get rid of the junk GM put under there, without the computer crying foul I will do so. Then I will make my own exhaust, using 5 inch stainless sections, and commercial grade flex pipe. I have used this set up for many hundreds of thousands of miles, on semis, so provided the computer allows, I will do it on this truck also. With the amount of room underneath the truck, I see no point at all in buying a ready made aftermarket system.

Update to the exhaust question.

On the trip to Phoenix my truck got its usual 4.5 mpg. But I had no power on the long grades out in Texas, New Mexico and Az. It is not safe or practical to run below the posted speed limit out on I-10. The dealer in Phoenix looked it over and pronounced the engine ok and said it had a transmission code, so over to Allison Transmission in Phoenix, no code was found and a bill of $224 for just checking it out. (Warranty Issue with GM). Both dealers said a larger exhaust was a waste of money on this truck. Dropped my trailer in Texas and on route to Fl. truck motor began to rattle intermittantly. Smoke poured from the exhaust white then black. Went to a dealer in Mobil,Al. listed in the one stop book was told they didn't have a desiel mechanic, was referred to Penniscola, Fl. and SANSING Chevy. Tech 2 was used but no code no problem and was told that if I wait till the next day a tech. could look at it. Called Chevy 800 number and got a case number and was refered to a dealer in the Jacksonville area. Made an Appointment for 7 A.M. the following Friday. I then drove the 100 miles to the dealer arrived at the correct time only to be told the only diesel tech was on vacation and I could get an appointment 17 day later and expect a 2 week wait. I called Gm Back and was given a dealer in Orlando area to take the truck to on the following Tuesday. It was running so poorly at this point I got in another dealer in Jacksonville who will look at it on the 7th. This makes the 6th dealer in 10,000 miles and 60 days of ownership. The Big exhaust will not help. The Rv trailer and truck have not change gross weights from 23,650 lbs. This truck has serious problems.