steering at highway speeds

Most likely grooves in the road is all.

 

relax and go with the flow. Fighting it will cause you to lose control.

 

? Are you drivin a full conventional cab/sleeper or a daycab?

Observation. The "fighting" to keep the tractor moving in a straight line has some to do with wind direction and speed; the road conditions; wheel balance and alignment; and yes your actual mph speed.
example: you are driving along and you notice storm clouds ahead. then you notice the truck pulling real hard to left or right due to the angle of the wind. a head wind (from the front) will not affect steering to much but enough to need to slow down some or speed up per the speed of the wind to counter the drag/resistence being put against your forward motion.
If it was a cross wind (from either side of the vehicle) you will have to turn the steering in the direction of the pushing. the higher the wind speed the further you have to counter the movement but not so much to over correct when no resistance if felt like passing under an overpass or a stand of trees, but then you get the wind again on the other side. In these types of conditions it is best to slow down but not so much as to be a hindrance to traffic behind.
A tail wind (from the rear) is the best to drive with. great on fuel economy and not much resistance.

As to the wheel balance and alignment, if you are having to consistently fight the steerage, I would write it up and have maint. check the balance of the steers and check a full alignment (3 axle).
As to road conditions, youll have the "grooves" that will try pulling the wheels to either side of the lane. just dont counter the action so much as to over correct and cause more problems associated with such reactions.

remember this too... ever action that the truck does there is a proper reaction to counter what it happening. to much reaction and rollovers occur or really nasty wrecks happen, which in turn will cause you to lose your job for life and the pain of knowing there couldve been a different outcome.

just my 2c from experience

 

One thing not mentioned is your grip on the steering wheel. First, relax the grip. Second, even though you are using both hands, only use one as the dominant hand. The other hand should be looser, there if you need it. What can happen with a tight grip with both hands is your hands will be fighting each other. That will make it seem like you are fighting to keep the truck straight.

 

Are you driving a Pro Star? I had one for a few months, recently got a Cascadia. Huge difference in line holding, especially empty. I didn't realize how bad the Pro Star was until I drove this for the first time empty; not even funny how wiggly that thing was. Sure wouldn't wanna pull triples with it, especially light! When it was heavy (most of the time) it was fine, but after a few weeks in the Cascadia, I don't miss it. Plus, it doesn't feel like I'm gonna tip over on every corner...

 

I bet you have one of them trucks that have air ride suspenion in the front...we had a volvo that had that and you have to hang on to the wheel and pay attention to the road more.