I have been getting 14 mpg on the highway lately and I have no idea what it can be! I use to get 17 to 18 and I dont know what has happened. The only mods I have are home made CAI an E-Fan and a power wire. I upgrade my oil to synthetic about a month ago and replaced 8 spark plugs with champion copper core but they didnt seem to really need to be changed. I cant figure it out and this is all hand calculated. Please help me this is annoying the heck out of me and costing me alot of money in gas. I realize i am not gonna get gas mileage but 4 mpg difference is alot!

 

id be happy with that my computer says i average 9.5, and I hand calculated my last highway trip 3 hours away, only got 9.2 mpg. Its a 4.7 in a heavy *** truck, what can u expect!

 

I use to get 17 everything except for those few things are stock I dont know why it would just drop like that. Its not like I have big tires or anything like you do though because if I did I wouldnt really care

 

Wonder if your CAT is plugged

 

I rebuilt it cause I thought it could be something with that but that didnt seem to help

 

My 4.7 has never got better than 14 unless you baby it to the point you get run over on the interstate. We dont have anything flat around here but still.

 

The power wire might be causing more motion-lotion to be used than is needed. I took mine off months ago.

You rebuilt the cat?

 

No never have rebuilt the cat and this actually happened before I put more power wire on....

 

same here, when i first got mine new it got 17.4 all the time. since then it has never got over 15mpg.
now its horrible because of the 35s haha

 

I know its annoying. Wheres the real smart people on the forum when you need them hahaha