When I put my car in 4th and set the cruise control at 40MPH for example, the car would jerk back and forth and couldn't hold the speed(It would go up and down). In 6th gear, it didn't seem to be a problem, but it might have just been less noticeable...

It's still under warranty and the dealer ordered a new actuator. They were supposed to fix it today but dropped the part and now it is doing the same thing with the new part so, they ordered another one...

I was just wondering if anyone else has had to replace the same part...

 

Over 5 years. Never a problem with the CC.

 

jasonw: I noticed something similiar the other day. I tried to use CC at around 35 mph (empty road late at night) and noticed it wouldn't hold steady it would jump from 34-35-36-ish. But on the highway in higher gears it works perfect. I've only noticed it won't even engage in 1st gear (tried it in a 15 mph school zone), but I assume that is normal.

I wouldn't worry about it to much, it may very well be common/normal on our cars in the lower gears. I don't engage cruise control at that slow of a speed to really care, let me know what you report back though!