2016 5.3 V8 with 8 Speed loses 1 MPG

Badass69 · October 23, 2015

My experience is that it does not hunt when towing.

When it needs to downshift it does so seamlessly, without 'racing' the engine. When speed and grade requires it will downshift and stay downshifted without a fuss. I've done interstate hwy runs where it ran for miles in 5th or 6th, and lots of times where it ran long periods in 7th.

For sure it shifts less on the highway than older transmissions did.

If only they could make the annoying 2-1 clunk disappear. It is less harsh and much less frequent with the latest update, but still occurs occasionally.

Hmm interesting. Haven't noticed the 2nd to first clunk in mine yet at all. Mine shifted like rubbish when the transmission was cold but I had the wiring harness with the TCM's thermistor swapped and it's been good now. I think that I don't have the first to second bog and die on the first shift after a start anymore.... so that's a plus too. Truck still needs a custom tune but their is a couple more things I want the stealerships to do first and then it will get one.

robvas · October 23, 2015

The 8 speed 6.2 smoked the 6 speed 6.2 in TFL Truck's Ike Gauntlet. Let people talk trash about the 8 speed, especially the people who don't have one or have never driven one. What do they know?

robvas · October 23, 2015

The 8 speed 6.2 smoked the 6 speed 6.2 in TFL Truck's Ike Gauntlet. Let people talk trash about the 8 speed, especially the people who don't have one or have never driven one. What do they know?

SuperSize · October 23, 2015

Wonder if the tested with 22" or 20" wheels. That can easily make a 1 mpg difference.

Ddurbin2014 · October 29, 2015

I currently have a 2014 CC 5.3L SLT Z71 4X4 with the 3.42 gears, so I have the 6 speed at the moment. Surely one would think with this combination you would see a MPG increase going to the 8 speed. Guess we will see soon.

I'm considering ordering a 2016 CC Denali 4X4 with the 5.3 and I was thinking about getting the 22" wheels. I was wondering if anyone has any information about how much it effects MPG. I know its all subjective but I was just trying to get an idea. If it changes it by 2 or 4 MPG I may just stick with the factory Denali wheels.. any help?

hurricanoday · October 29, 2015

I went from the stock denali 20s to the 22s with bridgestones and haven't noticed any mpg difference. This is with the 6.2 8sp, not sure with the 5.3. Def no where near 2-4mpg, still get 20+ on the hwy and am averaging about 18. Don't have to exact scientific figures but pretty much the same before. Don't think it could "easily make a 1mpg difference" I also thought I read on here the oem 20s vs 22s are the overall same size?

I have read it is all about the 3.23

TxTruckMan · October 29, 2015

I went from the stock denali 20s to the 22s with bridgestones and haven't noticed any mpg difference. This is with the 6.2 8sp, not sure with the 5.3. Def no where near 2-4mpg, still get 20+ on the hwy and am averaging about 18. Don't have to exact scientific figures but pretty much the same before. Don't think it could "easily make a 1mpg difference" I also thought I read on here the oem 20s vs 22s are the overall same size?

Same here and I agree 100%. I got the 22's and noticed no change in mpg, but I have the 6.2L. Go for it, they look great.

redwngr · October 29, 2015

P285/45R22 32.2" 647 rev/mile

P275/55R20 31.9" 653 rev/mile

P265/65R18 31.5" 661 rev/mile

P265/70R17 31.9" 658 rev/mile

As the rim diameter changes, the sidewall of the supplied tire also changes.

eg 265 width of tire 70 is the ratio of width to height, with higher numbers resulting in higher sidewall, R radial, 17 is rim diameter

Changing to factory 22's from factory 20's (or from 17's or 18's) makes no significant difference in the overall diameter of the tire or the tire rev's per mile.

Since they are all the same revs/mile they do not have to supply different speed calibrations when changing the wheel diameter.

tire spec data from tirecraft website

Selecting different model of tire may make a small difference in specs

Tattooo · October 29, 2015

Most likely due to 3.42 gearing as the only option with the 8 speed and 5.3.

http://www.fueleconomy.gov/feg/PowerSearch.do?action=noform&path=1&year1=2016&year2=2016&make=Chevrolet&model=Silverado%20C15%202WD&srchtyp=ymm

http://www.fueleconomy.gov/feg/PowerSearch.do?action=noform&path=1&year1=2016&year2=2016&make=Chevrolet&model=Silverado%20K15%204WD&srchtyp=ymm

I was thinking the opposite would happen and it would gain 1 MPG but apparently it isn't.

The claim is that i speeds do get better mph then a 6 speed ?

Tattooo · October 29, 2015

Well I say they have something wrong as all of the 2wd 2016 seem to have the same millage as the 2015 4WD.

http://www.fueleconomy.gov/feg/Find.do?action=sbs&id=37012&id=34675&id=34677

Unless the new body lost a full mile per gallon on all of the 2016's

I would say the numbers are not right.

I dont think those numbers are correct either

TxTruckMan · October 29, 2015

GM has confirmed that the 2016 with the 8 speed loses 1 mpg WRT EPA numbers, but they claim that it will be a gain in real world applications. GM said that since the 8 speed is only available on larger, heavier, higher trims, that there is more weight - and you can only get the 8 speed with 3.42 gears. The 2015 numbers obviously represent the best EPA configuration possible - stripped down models with 3.08 gears. So it's slightly an apples to oranges comparison. All things being equal, I bet that the 8 gets at least the same or slightly better fuel economy as the 6 speed. In fact, didn't the 6.2L gain 1 mpg going from 6 to 8 speed? And a while back GM claimed that the 8 speed was like 3.4% more efficient than their 6 speed.

Tattooo · October 29, 2015

GM has confirmed that the 2016 with the 8 speed loses 1 mpg WRT EPA numbers, but they claim that it will be a gain in real world applications. GM said that since the 8 speed is only available on larger, heavier, higher trims, that there is more weight - and you can only get the 8 speed with 3.42 gears. The 2015 numbers obviously represent the best EPA configuration possible - stripped down models with 3.08 gears. So it's slightly an apples to oranges comparison. All things being equal, I bet that the 8 gets at least the same or slightly better fuel economy as the 6 speed. In fact, didn't the 6.2L gain 1 mpg going from 6 to 8 speed? And a while back GM claimed that the 8 speed was like 3.4% more efficient than their 6 speed.

I hope in real life it at least stays the same.....I'm in the market for a 16

raym0016 · October 29, 2015

I hope in real life it at least stays the same.....I'm in the market for a 16

I would bet it would stay the same or improve ~1MPG when comparing a 2015 5.3 A6 with 3.42 gears to 2016 5.3 A8 with 3.42 gears.

BeauTie · October 29, 2015

I happened to find some data at intellichoice that is a little interesting. They conduct testing on cars and calculate their own "real world" MPG ratings which they believe are more realistic than the EPA numbers. They have an estimate listed for the 2016 Silverado with the 5.3L and it's better than their numbers for the 2015 Silverado with the 5.3L. They don't show which body style they tested so I don't know if these are directly comparable (2WD, 4WD, reg cab, crew, etc.) but it's possible the difference (or part of the difference) between the 2015 and 2016 numbers are due to the 6-speed and 8-speed transmissions. I understand that not all 2016s have the 8-speed so I'm not claiming this is a definite difference.

Anyway, they show 12.7 MPG city, 18.0 MPG highway for the 2015 5.3L and 14.6 MPG city and 20.4 MPG highway for the 2016 5.3L. Incidentally, they tested a 2014 V6 Sierra and those numbers are 15.4 MPG city and 19.9 MPG highway.

I'm not claiming these are any kind of conclusive data but just thought I would mention them because I just ran across them.

http://www.intellichoice.com/1-12-2016-60013-56/2016-chevrolet-crew-cab-z71-lt-4wd-short-bed-4dr-extended-real-mpg.html

raym0016 · October 29, 2015

I happened to find some data at intellichoice that is a little interesting. They conduct testing on cars and calculate their own "real world" MPG ratings which they believe are more realistic than the EPA numbers. They have an estimate listed for the 2016 Silverado with the 5.3L and it's better than their numbers for the 2015 Silverado with the 5.3L. They don't show which body style they tested so I don't know if these are directly comparable (2WD, 4WD, reg cab, crew, etc.) but it's possible the difference (or part of the difference) between the 2015 and 2016 numbers are due to the 6-speed and 8-speed transmissions. I understand that not all 2016s have the 8-speed so I'm not claiming this is a definite difference.

Anyway, they show 12.7 MPG city, 18.0 MPG highway for the 2015 5.3L and 14.6 MPG city and 20.4 MPG highway for the 2016 5.3L. Incidentally, they tested a 2014 V6 Sierra and those numbers are 15.4 MPG city and 19.9 MPG highway.

I'm not claiming these are any kind of conclusive data but just thought I would mention them because I just ran across them.

http://www.intellichoice.com/1-12-2016-60013-56/2016-chevrolet-crew-cab-z71-lt-4wd-short-bed-4dr-extended-real-mpg.html

12.7 city and 18 Highway is woefully low compared to what I am getting. I get about 18 in mixed driving 60% stop and go and 40% highway. I have 3.42 gears 5.3L CC.