Does anyone else lose a bunch of gas mileage when they run the cruise control? I went from 18mpg with it off to 14mpg with it on. I guess that was money wasted option-wise. RCSB 4x4,4.7, 6 speed, 3.92 gears. First time this has happened and Ive owned every brand over the years.

 

Usually you will gain MPGs with cruise control. I know I gain with cruise but thats prolly because I don't have my foot in it.

 

I lose mpg too. I believe this is because, i know what kind of driving condition it takes to get decent fuel mileage. Knowing that, when i see hills or dips, or other conditions ahead, i can plan to adjust my driving accordingly. With cruise control on, your truck drives blind. When it drops into a dip, it lets off the throttle. When you go up the other side of the hill, CC lets the speed drop 5-7 miles and hour, then throttles up, bogs down, burns unnecessary fuel, then down shifts, again wasting unnecessary fuel.

When Im the freeway however, I set the cruise at 75 with tow haul. (2004 QCSB 4X4, 4.7) 18 mpg all day long

 

it looses it on hills for me, but driving home from the gf's this morning at 63mph i was getting 19.5 average on the overhead

 

I don't know how yours is, but it could be from a 6 spd. Would the loss of the ability to downshift affect it? Going up hills and having to speed up in a gear, bogging down, and still trying to regain speed. That's all that I can think of on this subject.