I am a new member and this is my first posting. I have an '05 GMC crew cab 4x4 that I bought in June and so far I'm lucky to 13 mpg. Is something wrong?

The truck has about 4500 miles on it. I mostly drive it in town, and a good percentage of the highway miles are towing a 6000lb travel trailer. With the trailer I usually run about 65, without around 70. I've been told that it will get better after break in, but I can't believe it will increase 6 or 7 mpg.

One more thing, the manual says tow/haul is designed for 75% of GCVWR. My trailer doesn't put me there, but I like the braking. Is this hurting anything.

towing? empty? city? highway? what speeds? w/o knowing details hard to tell. stop and go intown your in the ballpark. unloaded all constant highway @ 65-70 you should see 17+

Just did a roundtrip from Elko to Vegas including 2 days in Vegas traffic. No tow, light load and 68 to 70 mph on highway. Mileage was 17.9 overall. Got fuel in Vegas at Shell for 2.99 per gal but most fueling stations were 3.20. 3.20 here in Elko now.

Just did a roundtrip from Elko to Vegas including 2 days in Vegas traffic. No tow, light load and 68 to 70 mph on highway. Mileage was 17.9 overall. Got fuel in Vegas at Shell for 2.99 per gal but most fueling stations were 3.20. 3.20 here in Elko now.

I am getting close to the same milage as you.

Wish it was around 20MPG on FWY.

So what modes do we need to do to get to that 20MPG?

Welcome to the site! You'll find MANY interesting topics to read about here. Fuel mileage is commonly talked about on this site especially since this latest leap in fuel prices. Try a search on "mileage" and you'll find plenty to read. I've noticed a lot of variability when it comes to mileage posted by members. Keep in mind that driving preference ("stole it" or "granny"), road conditions and terrain, weather, load weight or unloaded, tire size, vehicle/engine performance upgrades, bed cover, 4x4 or 2WD, truck size, etc., etc., etc. will greatly influence results. Since it is unlikely that all values for these variables will line up with someone elses, means you need to take other's results with a grain of salt. Also, the break-in period for the Duramax ranges from 10k to 25k miles and your fuel economy will change during this period. Good Luck and enjoy the site.

Oh, I suppose I should list my mileage. @ ~3600 miles, I'm getting ~17.5 mpg. This is 75% at 70 mph and 25% nearly non-stop town driving at 45 mph. The DIC and hand calculations are very close. I am noticing a very slight increase over the first 3600 miles. This is on the truck listed in my signature. My dad has an '03 Chevy LB7 Ex-cab Standard Box with 65 hp added via programmer (I can't remember which right now). He claims 18-19 @ 80 mph and 22 at 65 mph ... but always drives like he stole it.