2014+ Gas Mileage (MPG) Topic

Mike1220 · May 13, 2014

You're missing a relay wiring harness. See diagram attached to post #1 of this topic.

Honestly I have no idea. I have the paperwork somewhere in my room and if I can find it I'll let you know. I just know that the dealership sells many different aftermarket truck parts, such as the AFE intake W/ K&N filter, magnaflow exhaust, and the skyjacker level kit that I had them put on my truck before I picked it up. If I can find the paperwork I will share the model/part # and series

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Newm · May 13, 2014

Just filled up again...running all week with approximately 30% city driving I averaged 17.85 MPG figured by hand with DIC showing 18.2.

Mad Max · May 16, 2014

Sorry - long thread and I probably may have missed something. Is there anything that should be done/you would do right away with my 5.3L to improve the MPG? CAI sounds like a waste and the dealer said an aftermarket tune immediately raises flags for warranty. Still I'm pissed that the speedo goes to 140 and the truck has a 99mph gov on it, not that that would help my mpg - LOL. Magnaflow exhaust? Headers? Would those still be what y'all recommend and having any luck with? FWIW I live in a 30MPH town and get crappy mileage here an in Boston, but on the clear highway 21-22mpg or better is no problem.

Mike1220 · May 16, 2014

Sorry - long thread and I probably may have missed something. Is there anything that should be done/you would do right away with my 5.3L to improve the MPG? CAI sounds like a waste and the dealer said an aftermarket tune immediately raises flags for warranty. Still I'm pissed that the speedo goes to 140 and the truck has a 99mph gov on it, not that that would help my mpg - LOL. Magnaflow exhaust? Headers? Would those still be what y'all recommend and having any luck with? FWIW I live in a 30MPH town and get crappy mileage here an in Boston, but on the clear highway 21-22mpg or better is no problem.

Not sure about headers. But changing the exhaust and the air intake to aftermarkets that are less restrictive can help the mileage. Also if you wanted to squeeze every bit that you can, you could lower the back end a bit to level or come closer to leveling with the front and then install a skid plate that covers as much under the vehicle as you can cover. Should help squeeze more mileage. It would help more on highway than in the city tbh. Also try not to carry anything in the truck that you do not have to carry.

Probably the BIGGEST factors, or atleast in my testing they were:

Cut idle time to a minimum, don't Start the engine until your ready to roll

Radio, this can affect how you drive, by this I mean try listening to more of music that keeps you relaxed more than something that would cause you to gun it all the time

Map out your trip as efficiently as possible. Traveling a route that takes you 5 minutes longer is better if it requires you to stop and go less than a route that takes less time but has a few extra stops. This also contains the advice that the 'fastest' route, isn't always the shortest or the most efficient

And the biggest factor of all! Driving habits!

This is not to say that you are a bad driver or a speed demon, but as previously stated and as you've probably been told by several others before, easing into the accelerator and getting up to 30 mph over the course of say 10-15 seconds is much much easier and less stressful, and therefore far more efficient, than if you were to try to get from 0-30 before the next time you have to blink!

I have adjusted my driving habits since I got the truck. I turned a 15 MPG / 20 minute / 14 mile trip to school in the mornings into a 17-18 MPG trip / 24 minute / 16 mile trip.

These numbers are an average over the course of around 10 trips for each route, almost identical time of morning, almost identical outside temps, identical traffic patterns

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Mad Max · May 16, 2014

Not sure about headers. But changing the exhaust and the air intake to aftermarkets that are less restrictive can help the mileage. Also if you wanted to squeeze every bit that you can, you could lower the back end a bit to level or come closer to leveling with the front and then install a skid plate that covers as much under the vehicle as you can cover. Should help squeeze more mileage. It would help more on highway than in the city tbh. Also try not to carry anything in the truck that you do not have to carry.

Probably the BIGGEST factors, or atleast in my testing they were:

Cut idle time to a minimum, don't Start the engine until your ready to roll

Radio, this can affect how you drive, by this I mean try listening to more of music that keeps you relaxed more than something that would cause you to gun it all the time

Map out your trip as efficiently as possible. Traveling a route that takes you 5 minutes longer is better if it requires you to stop and go less than a route that takes less time but has a few extra stops. This also contains the advice that the 'fastest' route, isn't always the shortest or the most efficient

And the biggest factor of all! Driving habits!

This is not to say that you are a bad driver or a speed demon, but as previously stated and as you've probably been told by several others before, easing into the accelerator and getting up to 30 mph over the course of say 10-15 seconds is much much easier and less stressful, and therefore far more efficient, than if you were to try to get from 0-30 before the next time you have to blink!

I have adjusted my driving habits since I got the truck. I turned a 15 MPG / 20 minute / 14 mile trip to school in the mornings into a 17-18 MPG trip / 24 minute / 16 mile trip.

These numbers are an average over the course of around 10 trips for each route, almost identical time of morning, almost identical outside temps, identical traffic patterns

Sent from

All great advise much appreciated thanks! Trying not to gun it isn't easy in a new truck that flies but I know that the tires, brakes and everything else aren't inexpensive to replace either. Stock 20" AT tires are what $250? Skid plates came on the LTZ Z71 - it's one of the reasons I got it as opposed to the High Country (although I see now they are plastic!). Kinda hate to lower the back because it will sag when loaded up. But there are helper springs I've seen people here install that don't affect the height or the ride, so if I do both leveling and helper springs I'd be in better shape all around - slightly extra weight for that stuff but probably not much. Not keeping much in the back sept for a couple folding chairs, small tool box, fishing rod and golf clubs - LOL. And the occasional case of beer and a few stogies but hey... ;-)')

SlavO · May 16, 2014

2014 ;) 60/40

Cmillerjr · May 19, 2014

Just thought I'd put this out there. I changed the wheels and tires on my truck the same time it went in for the recall(18's to 20's) Before that I was averaging 16/17 city 19/21 highway. After the bigger tires it dropped to 13/14 city. Well the other day I noticed that all 4 tires were at 35 psi. I bumped them up to 37 psi (cold), and my city mpg's are back up to 16/17. I haven't driven any highway since but I'm sure that will go up as well. It's only 2 psi but it sure does make a difference.

Audioi · May 19, 2014

Just thought I'd put this out there. I changed the wheels and tires on my truck the same time it went in for the recall(18's to 20's) Before that I was averaging 16/17 city 19/21 highway. After the bigger tires it dropped to 13/14 city. Well the other day I noticed that all 4 tires were at 35 psi. I bumped them up to 37 psi (cold), and my city mpg's are back up to 16/17. I haven't driven any highway since but I'm sure that will go up as well. It's only 2 psi but it sure does make a difference.

My came new with 20" and they had 39 psi, I have kept them at the 39psi and like the MPG!

Edited May 21, 2014 by Audioi

Newm · May 20, 2014

Just filled up again last night. Seems like my "normal" driving routine with about 30% of it being city driving is putting me around 17.8 MPG. And that is even with a couple 0-80 MPH runs.

Man I love this thing!

cansled · May 20, 2014

I know this shows 25 mile, but the average was even a little higher for my 60 mile trip. The first 25 miles was 21.5. This is with no exhaust flapper and resonator, with a GMPP muffler. Pretty happy with the results.

softail_silverado · May 20, 2014

Just hit this over the weekend. Highway miles on stock truck 65-75mph. I certainly can't complain.

My day to day commute is only a few mile stop and go haul to work so it kills my mileage but if I continue to get numbers like this when I do actually hit the highway then it will keep me happy.

SlavO · May 20, 2014

Only way to really see what your getting is put it at the 400 miles .... And look at your trip counters, I rest every fill up and every oil change you can really see what your getting....

BTW.. My truck came with 20s". PSI Set at 40 I was getting great numbers. I drop the psi to 32 ride got way better but lost maybe 2 half mpg So I'm going back to 40 today

Newm · May 20, 2014

Only way to really see what your getting is put it at the 400 miles .... And look at your trip counters, I rest every fill up and every oil change you can really see what your getting....

BTW.. My truck came with 20s". PSI Set at 40 I was getting great numbers. I drop the psi to 32 ride got way better but lost maybe 2 half mpg So I'm going back to 40 today

I should really raise my tire pressure and see what that does to the numbers. They are set right at about 34 PSI right now. I will raise them to 40 and see what happens.

galliher_nc · May 20, 2014

My 6.2 is getting 14.6 according to the DIC with just over 2,100 miles on it now. 70/30 city/highway.

TxTruckMan · May 21, 2014

I have my tires down to 30 psi cold and I'm averaging 17.5 in mixed driving. My tires were near 40 upon receipt, and the mileage was the same. I don't think tire pressure makes as much of a difference as you're giving it credit for. I'd expect less than a 1 mpg hit as long as they're not too low. Anything below 30 is getting low.