Hi ya'll I'm new to the forum.. .. I love my GM vehicles I have a 1995 K1500 Silverado 208,000 +miles (my daily driver) 21.5 mpg was my best with this truck, 5.7L / 4L60E / 3.42 gears.

My new truck is a 2010 GMC Sierra 1500 EXT-CAB SLT (All-Terrain Pkg) Z71 4X4, one SWEET Ride!!! I have the 5.3L with the 6L80E (6-Speed) tranny and 3.42 rear-end. I took a trip 90% interstate driving around 60+ miles and I averaged 24.7mpg. This only has 1,100 miles on her. Shes 100% stock, I did have half the gas tank 87 octane and filled up the rest with 93 octane when I did this run.

I'll try and post pictures of her....in the mean while I tell a little more about it; onyx black, ebony/titanium leather seats, heated and memory seats, basically everything but navigation and sunroof.

Tell me what ya'll think?
Daniel

Damn..... that's some awesome fuel economy!

I'm lucky to get 18 MPG highway on my '08 with the 5.3, 4-speed and 3.73 gears.

I just took my first road trip this weekend that didn't involve towing something, and I was surprised at the mileage. I even did about 30 miles of low speed 4 wheeling, and with the same truck as you, I got 19.9 mpg. My DIC is usually off about .5 mpg, so even then, it's be over 19 mpg.

I also took the chin spoiler off, as I was afraid some of the stuff where I was going might remove it for me.

I took this on my way home from work today. 4.8l 4 speed trans. Crew Cab

The photo is a little fuzzy because I had the windows down and I was trying to not run the person next to me off the road.

sorry but i am having trouble believing that you got over 20mpg with a 350.....

Looks like you guys are gettin pretty lucky with the mileage. I have been tracking mine since day 1 and I am nearly completely an interstate driver. My overall mpg is right at 16.2 now at nearly 9k miles. My best tank was 20.3 (tailwind) with a low of around 13.5 (headwind). I also have the LH6 5.3L in a crew cab z71 4X4 with the 6L80E and 3.42 gears. I am however definitely seeing an improvement in my overall mpg now that the summer blends are hitting the pumps. Wonder if the VVT is helping the numbers for 2010 trucks some. Just as a note I ran three full tanks of 93 octane as a test and didn't see any improvement or decline in my mpg so I switched back to 87. I may have to do another test on the summer blend to see if there is a difference.

I am getting 28 out of mine with the same set up.


(please note that I did not specify 28 of what )

are we driving 55mpg or 85 mpg (like most of us) ?

WOW you must not have a foot like mine.

ok soo really 25 mpg in that pic... hmm kind hard to believe knowing i only get 13-15 mpg. How accurate are those things. I have yet to see one very accurate at all.

This is 100% true I did indeed recieve 21.5mpg with my 1995 K1500 350 engine. This was slighty less than 100 mile trip of 55-60 miles-per-hour of interstate. I filled up the tank with 93 octane right before I started the trip, reset the trip meter, than on the way back filled up took the miles driven divided by the gallons took to re-fill the tank which equaled around 21.474 (something in this nature this was a while back). You've got to be SUPER EASY on the gas pedal / a little hypermiling. Now when I averaged a full tank I got little above 19mpg.

This was 55-60MPH trip only!

Something is broken with mine. I have never gotten above 18.1 mpg average and that was a flat 400 mile trip both ways empty on a nice day. I have a 4.8 4spd with 3:42 rear. Not that I'm calling you guys liars, but I average 13-14 mpg each and every tank, about 75% highway and 25% city.

Ok, my honest mileage is about 15 MPG city, and 17-18 MPG highway when cruising around 75 MPH. That's an '06 crew cab Z71 4x4, 5.3, 3.73 gears, no AFM. I have never seen 20 or more out of this truck. All mileage numbers are based on refilling an empty fuel tank and dividing the miles driven by the number of gallons pumped into the tank, not some useless DIC display.

I use the DIC as a gauge...but do my mpg calcsa by hand when I fill up. DIC is off by about .5 mpg.

i dont trust the DIC i dont think its too accurate

Mine has been incredibly accurate so far. The DIC is showing an average of 16.2 and my spreadsheet tracking fuel rounds right to 16.2 mpg.

Nice Truck, can't wait to see some pics. I've got an '08 Sierra 5.3 EC All Terrain 4 spd , not sure what gear but have avgd 20.2 on the highway with a 12' aluminum boat & camping & fishing gear all in the bed of the truck, so I deffinitely don't doubt your good fuel mileage, you just have to be really easy on the throttle. my everyday driving, probably 60% highway 40% city I get closer to 15mpg.

I believe the mileage readout at these speeds. My DIC instant fuel economy on a flat smooth highway at 60 mph will read ~ 28 mpg. Unfortunately, I can't keep her much under 75 mph here in SoCal. Plus, where I live, I travel a lot of rolling hills and that cuts my fuel economy greatly. I'm happy if I average around 15 mpg when I go fill up. Pretty standard for a full-size truck.

I averaged 14.6 MPG with my 2008 4.8 without AFM. After installing my Borla Cat-Back it's been steadily rising and is at 15.9. I've been harder on the gas since the new exhaust was installed and it's still over 1mpg more.

Those readings are from the DIC and is from 95% city driving.

ok still, not going to call anyone liers here... but i wont believe 20+ mpg in a 5.3l untill i see it and divide it myself.(and kinda to make it clear, i dont think we are talkin about one trip mainly because someone could miscalculate there mpg in one trip.. saying they get 25 mpg then never reach it again, to me i think the mpg should be calculated then averaged with atleast 3 other trips)

BS....your not getting that good of gas mileage. I did a 100mile drive one day a few months back, drove 65mph the entire time, a/c off with vent open and cruise control. Started with a full tank.

I refilled the day and did the math like so,

miles driven divied by gallons to refill. I was able to get 19.9, the first 50miles had a slight down grade.

This is the first time replying to a post. Couldn't stand it anymore. You guys need to be more specific. I just bought a 2010 Silverado 1/2 ton 4by4 5.3L Aluminum block, 3.42 pos rear, six speed trany. I'm in Phoenix, moderate temps, 65to 80 degree temps. No rain so air is very dense, Driving around town at 35 to 55 mph. Then on highway not above 65 miles per hour. Really babyed the truck . First tank I got 17.75 mpg. Second tank when I did more seventy miles per hour 16.8 mpg. On a flat road little head wind at below 65 miles per hour you can keep the fuel mangeagement engaged so you are in 4cylinder mode. However above 65 miles per hour the increased load engages the other 4 cylinders so you are running on 8 cylinders. Running at 60 miles an hour flat road you should be able to stay on 4 cylinders forever. If I left anything out let me know.

Just hand calc'd mine this weekend, and it was 19.2, and I think I may have filled it up more this time, as I always try to get to even dollar amounts.

Guys i pull 16-17 with my 2000 3/4 ton Chevy 4x4 crew cab with a 6.0L and 4L80E. There's no reason a 5.3 brand new shouldn't be able to pull into the 20s with a 6 speed. Those 6 speed autos make a big difference. High power and torque at low RPMs for highway = we have a winner.

I have an 09' 4wd CC with the 5.3 aluminum block, 6 spd , and 3.42 gears. I recently took a trip 480 mile total.I reset my DIC as I left and got 22.6mpg on the DIC right as I was exiting from the interstate. After I crossed a mountain and arrived at my destination it had lowered to 21.9 mpg. That was traveling mostly intersate running 70-75 mph with some 55-65 mph highway mixed in. When I returned back home my total trip average was slightly over 20 mpg. There are more hill climbs on the way back.

is is just me or does everyone get completley diffrent mileage on the same engine? i know people have diffrent driving habits but no 13-14 mpg and 24mpg.... haha whats the real answer?

Driving habits and type of driving does make it vary quite a bit, along with hilly areas vs flat land. I've been averaging between 17-17.5mpg this spring. And thats probably an average of about 70% highway at ~55mph..I was getting around 16 all winter

Also different gear ratios in the axles as well as different transmissions.

I have found that the computer in my truck reads nearly 1 mpg high whenever I do the math manually so it's just an estimate being displayed on the dash and the wind conditions make a huge difference in mileage.
Also, how many of these people getting really high mpg only have 2 wheel drives, not 4x4 with the extra weight?

I can pull 6+ mpg difference depending on whether i keep my foot out of the carb.

WOW... am I the only one here that can spell the distinct smell of bullshit in this thread?

I don't see why everyone is so skeptical of 20+ MPG out of the newer trucks with 6-spds? Just because Toyota hasn't done it yet doesn't mean it's not possible. My 2000 GMC Sierra ECSB 5.3 4L60E 4x4 with 3.73 gears will pull off 22 MPG highway with a very light foot at 65 MPH. If I drive like a grandma I can pull off 16-17 in the city. "Normal" driving habits results in 13-14 city and 15-19 highway.

Actually I believe your post nails it. It is POSSIBLE to get good mileage out of these trucks but I average 16 no matter what. I don't pussyfoot around though and rarely do less than 80 on the interstate. I'm no road demon, that's just what the freeway traffic does here.

If you reset the DIC average, then coast down a long hill the average displayed will be really high, so it can be played with. I reset my average at every tank. Its 16.X everytime, every driving style. Calculating by hand nets the same result everytime. The only difference is if we have a lot of snow on the ground where I'm using 4 wheel drive or if I'm towing something. I have honestly witnessed one other truck get 21.X on the average, it was a GMT-800, probably a 2005ish with 5.3 ext. cab shotbed 2wd, I don't know the ratio on the rear end. This guy drives like a old man, 60mph on the highway max.

I don't believe the dic... you're not getting 98 miles to the gallon just because you are going down hill and off the throttle, no way. I've done all my calculations with calculator and I've never seen over 19.5 in my truck. I went over 250 miles from hartford ct down to philly and back up. with a head wind doing 64avg mph I got 18.91. Coming back with 50mph gusts (this past weekend) at MY BACK I got around 19.1 (probably about 20 really after i figured out i under-filled).

a 45mph gusty tailwind, doing around 65mph behind a tractor trailer.... about 20mpg... 12,000 miles on the truck.

I've recorded all but 2 fill ups and its about 17.5mpg.

I have 03 w/5.3 and 4.10s and I can get 18 on pure highway trip. Drove from huntington wv to chapel hill nc and got the same mileage both ways. In my old 02 5.3 w/3.73 i went from wv to colorado on trip and never got less than 18 cruise set on 70. One tank on that trip I got just over 21. It's all in the way you drive. my 03 with 4.10 will get 20 only if I'm going 60mph or less on basicaly flat ground. Only done it one time. Everyday driving mixed and very little highway I get 14-15mpg.

It says 98 down hill because the truck doesnt know any better. All it knows is that you are accelerating without any throttle imput and if you could maintain that you would get 98mpg. FYI, just because your truck wont get 20+mpg doesnt mean that its impossible to do with mine.

I didn't say you couldn't do it, i just don't believe dic is all.

I have a "DIC" on my 2009 Kawasaki C14 Concours motorcycle and there is "instantaneous mileage" and "average mileage". While I can see instantaneous mileage as high as 70 MPG when coasting, the average MPG is about 38-40 MPG.

That's almost exactly what I posted for a very similar truck with identical engine and gearing. I have not been able to get more than 18 MPG highway no matter what I do with my truck. Maybe is I cruise at 60 MPH with windows up and A/C off?

Believe that if you like but ACTUAL calculated mileage when you fill up will be more like 15-19 MPG.

I can really coax 20 mpg out of mine if I am very very very careful at highway speeds. Actual NORMAL mileage for me is closer to 16.

Read again, it's a motorcycle. It actually gets close to 38 MPG. And it does have a trip computer and even tire pressure sensors with display.

Read again, it's a motorcycle. It actually gets close to 38 MPG. And it does have a trip computer and even tire pressure sensors with display.

I record every drop of fuel in the truck and the overall average from the DIC and from my hand calculated mileage is not off even a single tenth of a a mpg. So far, I am averaging 16.3 mpg overall with almost entirely interstate miles running at approximately 70-75 mph. The DIC is very accurate from everything that I am seeing in my truck. Btw I have a 2009 Crew z71 4x4 with the aluminum 5.3 and 6l80e and 3.42 gears(comparable configuration to many others in the thread).

I wish I could agree with those who say the DIC is right on but hand calculations always net me at least a .3 mpg difference... sometimes a bit more.

Well son of a bitch. It is at that!

Keeping the MPH as low as possible with the windows up and A/C off will always net more MPG. You're reducing drag on the vehicle and engine by doing this.