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  1. #1
    Sr. Apprentice
    Join Date
    Jul 2011
    Mississauga, Ontario, Canada

    Default 4.8/4 speed vs 5.3/6 speed for in city fuel economy

    I've been looking at a new Sierra to replace my 2000 Sierra. After reading some posts on this site, it seems that many people with the 5.3/6 speed auto. tranny combination aren't getting nowhere near the EPA's fuel economy ratings of 15 mpg (15.7L/100 km) in the city. The 4.8/4 speed combination gets according to the EPA 13 mpg (18L/100km) in the city. The 5.3/6 speed combo is a $2000 option here in Canada where I live. So, what can reasonably expect to get in the city for fuel economy with the 5.3/6 speed combo? Is it worth it?

  2. #2


    My truck is new, less than 3500 miles but with the 5.3/6spd auto I'm averaging 16mpg city and 20mpg on the highway at this time.
    I started out a little lower but noticed with my last two fill-ups it's getting better.
    At a $2000 higher purchase price it'll take a while to pay the difference, but when I bought mine I would've gotten the 5.3/6spd even if it got a little less mileage after driving a 4.8/4spd while towing. It's not a huge difference but there is a noticeable horsepower difference and between my house and one of my favorite lakes theres a couple of large hills.
    I wouldnt buy the 5.3/6spd combo if all your looking for is fuel savings or 1-2mpg less is gonna make a difference to you, I would buy it if you haul heavy loads or trailers and you want just a little more power. As is usualy the case if you want more horsepower your gonna have to pay for it at the dealership and the pump.

  3. #3

    Join Date
    Feb 2008
    Red Wing, Minnesota, United States


    ALL brand new vehicle take time to get MPGs up, you have to get past that engine break-in point which some will say is 5000 miles.
    99 K1500 Suburban LT "THE BEAST"
    Hypertech III, K&N, true dual

  4. #4


    my 2009 with the 5.3 6 spd is just under 31000 and city i get avg of 16.5 mpg if you watch the indicator.

  5. #5


    I've had slightly mpg's depending on what city I was in. 13-15 city in Monterey, ca while I'm getting 14-16 city in Las Vegas, NV. Depends on roads, hills, and driving style. Overall, I believe it's a better bet to get the 5.3/ 6 speed, "better to have it and not need it, than need it and not have it."

    2010 GMC Sierra 1500 SLE Extended Cab Z71 4X4 5.3L Flex Fuel
    MagnaFlow single in duel out system
    Volant CAI & Ram Air Scoop with Power Core Filter
    Rhino Tuff Grip Spray in Bed liner
    Undercover Classic Tonneau
    Trail FX Bug "deflector"
    AVS Window Deflectors
    Black Powder Coated Nerf Bars
    RECON L.E.D. Interior, 3rd Cab light, Projector headlights, and Taillights
    ATX Crawl Wheels wrapped in BFGoodrich Rugged Terrain tires
    CalTrend Neoprene seat covers
    2" leveling kit from Max Trac
    Diablo Trinity with Diablew Tune

  6. #6
    Sr. Apprentice
    Join Date
    Jul 2011
    Mississauga, Ontario, Canada


    Thanks for the responses. I just use the truck for my part-time lawncare business on weekends. I don't do much towing with it all.

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