There were comments/questions on earlier posts regarding mileage after changing to 4.10 gears. I changed mine quite a while ago but have not checked highway mileage until last weekend since I am usually towing a trailer when on the highway.
Here is what I experienced:
City mileage improved from 15.5 to 16.7 in constant stop and go, 17+ in city with fewer stops and no load.
Highway at constant 70 mph went from 21 to 19.7. At 75 mph, it dropped a bit.

My Dak is an '05, 4.7, auto, QC.
The performance improvement is really worth the small drop in highway mileage and the increase in city mileage is a bonus. More than half of my driving is in the city.

 

how the hell were you getting 21mpg highway before? i can never get above 16-17 even when babying the heck out of it

 

I am pulling the same numbers all week long right now on the 3.55s... its all in the foot Hook me to a trailer and I lose probably 3 mpgs all around.

 

Cha!!!I can't hardly crack 18mpg highway..... you sure your truck has 8. Cylinders and not 6???

 

:icon_attentio n:

 

I ain't never seen over 20. city or highway

 

so you have a v8 and what size tires?

 

im lucky to get 13.5 in the city with the 4.7 and keep in mind thats babying the hell out of it, i havve no mods and 265/70/r17 tires with the 3.55 gears

 

huh? I am only averaging about 14-17mpg half city/half highway in a v6 w 3.55s. (heavely modded) Are you sure they put in 4.10s?

 

Ever since I joined this forum there have been big differences in fues lileage. Your left foot makes a big difference but I think there are differences in the trucks to. If you are getting poor mileage and driving to get the best you can, there must be a difference in the trucks.
I guess I'm one of the lucky ones that has always gotten decent mileage. Even pulling a trailer from Florida to Texas, I got 13.5-14 mpg with 4.10 gears.