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I own a 2014 gmc double cab truck.In the last six months I have had bad gas mileage. I changed the wire and plugs (AC Delco) Transmission Service and had changed the differential fluid change. My truck has 93,000 miles on it. I have always changed my oil on time. Nevertheless, I took my truck to my mechanic that I trust. They took it and at the end of the day told me that it is an internal problem with the engine and that I need to rebuild the engine. Has anyone else had this problem?

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I have a 14 DC 4x4. What mileage is considered bad to you?

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18 minutes ago, avidsailor said:

I own a 2014 gmc double cab truck.In the last six months I have had bad gas mileage. I changed the wire and plugs (AC Delco) Transmission Service and had changed the differential fluid change. My truck has 93,000 miles on it. I have always changed my oil on time. Nevertheless, I took my truck to my mechanic that I trust. They took it and at the end of the day told me that it is an internal problem with the engine and that I need to rebuild the engine. Has anyone else had this problem?

Go to Amsoil.com, get the engine and transmission flush product along with their power foam.  I recently did this and easily gained 1mpg city, 2 on the hwy.

 

Check your MAF.  May be due to get some MAF sensor cleaner from the store and clean it.  

 

See if a friend has a tuner or stop by local parts store to see if any codes are present.

Edited by btj_z71

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What real world mileage are you getting? Are you towing? I wouldn't rebuild an engine for fuel mileage it doesn't make much sense. It would be running like dog poop if it was bad enough to affect fuel economy.

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What is the internal problem that your trusty mechanic said was the cause? 

isn't the warranty to 100k? If you know the exact cause, take it to dealer, it may be covered.

 

Besides that, do CRC intake valve cleaning and sea foam fuel treatment to unclog injectors, Lucas products... there are options.

Change gas stations, use 93 for a bit to see if that helps. Cold temps dont help with mpg either.. 

Edited by Ozer

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I own a 2014 gmc double cab truck.In the last six months I have had bad gas mileage. I changed the wire and plugs (AC Delco) Transmission Service and had changed the differential fluid change. My truck has 93,000 miles on it. I have always changed my oil on time. Nevertheless, I took my truck to my mechanic that I trust. They took it and at the end of the day told me that it is an internal problem with the engine and that I need to rebuild the engine. Has anyone else had this problem?
Have them do a compression/ leak down test. List the numbers and find out what they are from the factory.

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