Lower mpg, running rough 2010 Tundra 5.7L 35k

2010 Tundra 5.7L with 35k original miles.

Parents truck that doesn't get driven much. Running rough, shaking a lot. About 12mpg. Seems to get worse as the gas gets lower in the tank. I looked for the inline fuel filter. Guessing it's in the pump. Some times fuel injector cleaner helps, but get to end of tank and starts running rough again. Any thoughts? I don't want to redo the injectors if it is something with the gas/pump/filter that needs addressed first.

I'm open to all thoughts.

Also, What is the easiest way to drain the tank? Is there an easy port to access on the tank to get a pump into the bottom?

 

Check out the reviews on Royal Purple Max Clean. It’s worked great for me. You will need more than one can, since 1 can does 20 gallons. The best way to use it is to add it to the tank, then fill, then take a long drive at one time using at least 1/2 tank. May have to do it twice. Good luck

 

What is the tank size on a 2010 5.7l?

 

I think it’s 26.4

 

Even though you have low mileage, it probably wouldn’t hurt to change the plugs & PCV after 14 years.

 

Clean the throttle body, replace the air filter, pour 2 cans of Berryman's B12 in a half tank of gas and get it out on the highway from 60-80mph for a couple of hours.

 

Try cleaning the MAF.

 

You are barely driving 3K miles a year. Are you sure you don’t have some skunky gas in there. If you are barely driving it , it wouldn’t hurt to keep the tank full with some fuel stabilizer in it.

 

Is it a Flex Fuel 5.7?

 

I just got a 2010 5.7 with 325000 KM on it. It gets 22 mpg. But thanks to you all for the direct instructions
to give it an initial tune.

 

How are you getting 22mpg? Was something changed or upgraded? It's only rated for 16mph highway?

 

No, I'm old and drive consistently. It goes downhill fast when I go fast. But that's what I get just puttering around
and on the open road with no load.

 

He's got an RCSB so it's a good bit lighter than most

 

its not in km/gal?

 

When you say running rough what do you mean? Does it smooth out as the rpms go up? Does it rev up normally?

 

The best I have ever got was 17.5, but as soon as I go over 70 it will drop to a little above 15. My work truck is a 2023 Sierra with the 2.7 Turbo 4 cyl. That gets around 25 if you keep it under 70. Over 70 it’s around 20 MPG. I will say that I’m shocked with the power it has, but I wouldn’t expect it to last over 150K before it will need some major work. You can hear the turbo whine every time you give it even a little gas

 

Nope.

 

That would be like 13.5 Mpg which would be terrible

 

Have you checked the air filter?

 

Any codes?