I have a 2006 Monte Carlo LS that when driving on gravel roads tends to "sway/swim" when going about 40 mph. The tires I have currently on only have about 8000 miles on them and still have good tread remaining. This problem seemed to start after the last tire rotation I had done. I put the tires back to where they were at prior to the rotation and didn't make a difference. Have checked wheel area and everything seems tight as well as check trailing arms, with everything looking good. Any ideas of what may be causing this problem?

 

This may sound a little stupid but did you verify the air pressures? I feel sure that would have been the first thing you did but thought I would at least ask.

 

Yes, they all had the same amount of tire pressure, 35lbs.

 

The wheels shouldn't be a (seems tight) thing. The wheels should be torqued to the proper specs usually around 100 ft. lbs. get a torque wrench to make sure.
Otherwise this will end up warping your rotors.
What does it do on the regular highway? Gravel roads are horrible we have a bunch in NE and also in IA and they are all crap.
I used to do inspections on gravel roads and depending on the road grader operator they were always similar to off-roading. I personally won't even let go of the steering wheel for a second on Gravel. I usually travel them for hunting.

I would check the condition of the Tires, make sure they are all wearing straight, Check the balance of the wheels you could have had some (smart aleck) stick some weights on the wheel in the wrong place.

 

On regular highway, it drives fine. The only time I noticed an issue on pavement is when on a highway or bridge and although it looked dry, might have been a patch of ice. From NE and the gravel roads can be horrible. Lately, the gravel roads have been dry and solid, so not snow/ice covered or muddy. Yes, our gravel roads in some cases are like driving on a wash boards or have ruts from previous muddy times, but this happens when it is "relatively" smooth and dry. The tires look to be wearing straight and haven't noticed them to be terribly out of balance as that is can be pretty noticeable as the steering wheel vibrates more than normal. Actually have recently put on new winter tires on the front only that are (I think) balanced correctly, and the car still acts the same.

 

Did I read this correctly that you are in NE.
If so what part of the State. I am in NE as well. I-80 and 81.
I would like to get a Monte Carlo club started in the state.