Gas Mileage Changes when Transmission Acts Up?

ndking1126 · July 10, 2019

I sent my Silverado back to the dealership to have them do the two service bulletins on the 8 speed transmission (fluid change for shuddering and reprogram for hard shifts) and they didn't do it because they said they couldn't duplicate it (even though the technician felt the hard shifts in the car with me... not the point of this, however). I haven't had time to take it back in, so I've just been dealing with it for right now. I've got about 1900 miles on it.

I drive about 12 miles down an interstate and then about 10 miles down a parkway (at about 60 mph with only a few lights - it's mainly open) to work and back. What I'm starting to notice is that when the transmission acts up, the gas mileage seems to be about 1-2 mpg worse. Of course, the transmission isn't considerate enough to act up for a whole tank and then stop acting up for the next whole tank, so its hard to verify. I have noticed that when its acting up, I can't seem to get it to hoover above about 19 mpg over a 25 mpg average, but when it's smooth and acting normally, it hoovers around 20.5-21.

Has anyone else noticed this or am I imagining things?

HondaHawkGT · July 10, 2019

Not sure what you're talking about as far as "acting up". You're probably feeling the engine switching between different modes of DFM and thinking that it's the transmission acting up. Depending on what DFM mode it's in, fuel economy will vary.

f8l vnm · July 10, 2019

Might be in your head. No disrespect

ShamrockShooter · July 11, 2019

You are seeing the truck dropping cylinders. Mine does it too. It will say 19 the jump up to 25 even though my speed is on cruise. I've noticed the 8 speed likes to be driven harder. Under light throttle I get lots of clunks and rough shifts, but it seems smooth as silk if you give it some gas. Or try sport mode

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ndking1126 · July 12, 2019

I know what torque shudder and hard shifts feel like. Driving the same route back and forth to work with the same driving style some times the transmission is smooth and easy to drive. Sometimes it randomly start shuddering and giving hard shifts. What I'm talking about is not a problem with the cylinders shutting off.