I bought my Duramax in July '04 used with 35k miles on it. I was/am seeing about 11.5 mpg's (all city driving with short little trips). It has a 6" lift with 36" tires. I'd always assumed the mileage was killed by the larger tires, but after reading about others truly getting 18-19, now I'm curious. I am mostly curious as I have noticed something that makes me very nervous. When trying to accelerate it bogs down between 2000-2500 rpm and won't allow me to accelerate. (I am putting in fuel additive during the cold weather) If I keep it below 2000 rpm, everything's fine. It bellows out smoke too if I let it bog down. I have not changed the fuel filter since owning (36k miles now), not sure what the previous owner has done, so that will be my next task on monday. To make matters worse, my gauges stopped working tonight. I get backlight, but none of the gauges in the cluster work and I can't see any blown fuses on the side fuse panel. Could not find the exact one for the Instrument cluster there???

1st change the fuel filter,
2nd lose the 36" tires and suspension lift. Your mileage will improve.
Since you are at 36K at take it ASAP to a GM dealer and have them hook it to a tech2 and let them see if anything jumps out so it can be covered under warranty. If it's just a little over 36K, the dealer will fix it free of charge.

It does sound like the fuel filter is plugged, at the very least...

With all city driving and "short little trips" - it is plausible that you would be seeing mileage around 12-13 mpg with or without the tires and all... Add in winter blend fuel, and that drops fuel mileage a tad more.

The engine does not perform with efficiency until it is warmed up. And it is so damn efficient that it takes a long time to do so. Also, transmission doesn't lock up and slips until it reaches operating temperature. I get around 14 mpg with my commute to work (sometimes 13-ish). It is 1/2 mile to freeway - 7 miles on freeway and 1/2 mile on city streets to work. Doesn't reach full operating temps until mile 5 or 6 down the freeway.

On one trip up to seattle (150 miles from portland, oregon) when the truck wasn't even broken in yet I got 19.5 mpg - that was at just under 70 mph average speed. If you go above 70 - efficiency drops off real fast...

- jeff

what about the stupid gauge cluster stop working? Anyone know exactly which fuse it is? I've checked the ones that I think it may be, but they all seem good. That just started today. I hope these aren't signs of things to come.

Have you looked at the gauge on the air box to see what it says about the filter or looked at the filter its self. If you have a K&N or that type i would change to the OEM or Baldwin. Baldwin is a lot cheaper, filters just about as good as the OEM but has a shorter life. Foam type filters are good for performance but don't filter the dirt out near as well as top grade paper filters. Wix has a decent air filter to, but no Fram's. Dealers will kill you on filter prices. Don't run the truck with air filter off, its like huge vacumm cleaner and sucks up anything close. If that happens its buy-buy turbo and maybe more. Like one of the guys says, have a dealer put the machine (tech 2) on and also have the dealer run the VIN for maintenance history.

Do a Search of "Guage Cluster not working" and related words.
Other's have had some issues too. Try starting and stopping and then restarting a few times it might clear up.

Sound like the cluster is bad or has a bad connection. check all the filters.

There is a flash to correct the cluster inop, it just went to sleep and needs to be woken up. To wake it back up you must pull the cluster fuse for a second and put it back in.

It could be your 36'' tires as your speedometer and odometer are off and if system is not calibrated you will show less miles than actually traveled

do you know which is the exact fuse that will fix the problem? I have looked and there seems to be a couple different ones it could be. Is it in the cluster gauge panel on the side of the dash or the cluster under the hood......

Instrument Panel Cluster (IPC) Gauges Inoperative (Reprogram IPC) #03-08-49-020 - (Nov 19, 2003)

Instrument Panel Cluster (IPC) Gauges Inoperative (Reprogram IPC)

2003 Cadillac Escalade, Escalade ESV, Escalade EXT

2003 Chevrolet Avalanche, Silverado, Suburban, Tahoe

2003 GMC Sierra, Yukon, Yukon XL

Condition

Some customers may comment that upon vehicle start-up, all instrument panel cluster gauges are inoperative.

Cause

During a cold start or low battery condition, a low voltage condition may cause gauges to freeze during crank cycle.

Correction



Important

DO NOT REPLACE the following clusters unless a reprogram does not correct this condition.

15182138
15182139
15182140
15182141
15182142
15182143
15182144
15182145
15182146
15182147
15182148
15182149
15182150
15182151
15182152
15182153
15182154
15182155
15182156
15182157
15177467
15177468


A new service calibration has been released to correct this condition. Reprogram the IPC using the new service calibration, which was available from Techline starting November 3, 2003 on the TIS2000 version 11.5 or later. This calibration is an electronic calibration and is not available from GMSPO.

Warranty Information

For vehicles repaired under warranty, use:

<TABLE width="100%" border=1><TBODY><TR><TH vAlign=bottom align=middle>Labor Operation



</TH><TH vAlign=bottom align=middle>Description



</TH><TH vAlign=bottom align=middle>Labor Time



</TH></TR><TR><TD vAlign=center align=middle>N4199



</TD><TD vAlign=center align=middle>Instrument Panel Cluster (IPC) Module - Reprogram



</TD><TD vAlign=center align=middle>0.4 hr



</TD></TR></TBODY></TABLE>

FIGURE Power, Ground, Serial Data(c)


http://service.gm.com/engif/000/000/865/865514.gif

Whoa, sorry that pic is so huge... just pull the "IPC/DIC" fuse underhood for a second, and it will wake up.

well, to update all and put some closure on this. Took it to the dealer and they charged me $80 to flash the IPC as per the tech note. That did not resolve the problem so they wanted $495 to replace the entire unit. I drove it down the street, pulled the fuse out and low and behold, things started working. People like you all make the internet a very useful tool. Thanks a ton.

Now, off to draft my nasty letter to the manager of the dealership

Don,t forget the Generals bulletin that states "if the tire size isn't correct no warranty work is to be done on the vehical, until corrections are made" and remove any power enhansement devices too!

drive safe.

Having the same problem with my speedometer, sometimes will work and sometimes will not. The Chevrolet Service Dept said the cluster was bad and would have to be repaired or replaced. Only problem is they did not have one available. Told me they could take mine out and it would take about ten days to repair.

I have 35" tires on my truck and if I go by the display in my dash, the best I have gotten is 16.8 mpg. You have to figure for your speedometer for being off around 10mph going down the highway. I'm guessing about 2mpg. I guess I'm probably getting 18-19mpg. I also have thye edge programmer which did make a difference on the fuel mileage.