I just changed my oil and cleaned my air filter and Now my dic reads about 20 mpg highway. Before it was about 16

I know the dic is not correct cause my efi live. But could I really notice that much more mpg from what I just did??

I didn't.

Call me crazy, but wouldn't 16 to 20 be 4 more mpg???

I used snake oil and got 25 MPG :)

if it works for you keep doing it

those were ball park numbers

If you reset your AVG fuel economy, I'd give it a few weeks before you celebrate. When I reset mine, it tends to be high soon thereafter and then works it's way down to a true average as you encounter more driving conditions.

Its still a 40w at operating temerature...and no 4mpg is not likely from your oil, but more likely due to the clean air filter. Most common "fleet" results from changing to a quality synthetic like the rotella will result in maybe...and i mean maybe 10% increase in economy. I have over 15yrs. experience in the lubricating oil field, and more than that in fleet servicing, and never seen such an increase. Also, watch out for "boutique oils" while you may see an increase in mpg, i promise you that oil is lacking in another area like wear. Start running oil analysis and you will see what I mean.

Well we went on a 300 mile trip to the lake and normally the dic says 15mpg avg on the highway going 75

This time is was 16.4. So the increase was less but I'm sure most of it was the air filter being clean

But 16.4 is still dam good for 8100 lbs and 38 inch tires

it hapened to me also.i gained around .75 mpg with the new michelin ltx a/t2 tires .i just laugh at my friends,and my son who drive dodges all chiped up..im stock with around 65,000 on my 08 ..im getting around 16 pulling my 22' enclosed trailer loaded..it all depends on how you take off ,keep your foot out of the gas..just take off easy , and let the big dog eat.....