Well we just got home last night from a 961 mile trip. Averaged 20mpg.

2008 4x4 QC SLT. With a 4.7l.
Mobile1 5-20.
K&N CAI
Flow master 3"
Stock tires & 35 psi

 

If you have a tuner you can do all kinds of things, but the op only asked if his specific mods should cause an rpm variation at idle and cruising, an the mods didnt include a tuner. I suspect that your better gas mileage came from you trying to get better gas mileage, because I see no reason an idle change, or a rev limiter change would do that, especially the rev limiter, unless your checking gas mileage at wide open throttle

 

Im very aware of what the OP said i just added that i had the change when i insalled my tunner, some one else said some thing about a tunner i dont see you quoting them....

And since i have most of the same mods he does i was just throwing my opinion out there.

 

Thanks for the input, I didn't think that would be the cause, but I definitely noticed a difference, wanted to see if anyone else had noticed anything similar. And I was trying to get the mpg thread back to talk of mpg's instead a spark plug war... haha...

 

just got back from a 600 mile trip. 95% highway cruising between 65-75 got 17.8mpg when arriving home.

 

That's pretty much exactly what I get on my 300 mile trips home. Same speeds

 

I wasn't criticizing anyone...But the op asked a specific question and all the answers he was getting contained tuners, which he didn't have

 

Towing travel trailer weighing just under 8500# at 68mph for 200 miles at 10.03mpg. Computer said 9.9 and is always very close for me.

 

checkin in! mostly highway 120 mile daily route @60mph 5.9 magnum averaging 14.4mpgs

 

I drove 700kms round trip highway. On the way there I set my cruise at 100km/h on the dot and was getting 20.2 MPG. On the way back, I set it at 108km/h and I was getting 17.1 MPG.

I reset it when I entered the city and started getting 8.9 MPG. Poor Hemi.