This is for your specific car. This is what the GM techs use to find possible solutions to similiar problems like you are having. This is for poor directional stability and vehicle leads/pulls. I did not see any other info that might pertain to this.
It's a lot of info but if none of this solves it I'm not sure anyone can help you.
Poor Directional Stability
Step
Action
Yes
No
DEFINITION: Driver is unable to maintain consistent, predictable vehicle driving control in any direction.
1
Did you review the General Description and perform the necessary inspections?
Go to Step 2
Go to Symptoms - Suspension General Diagnosis
2
Verify that the directional stability is poor.
Does the system operate normally?
System OK
Go to Step 3
3
Ensure that the tires are all the same size, make, and adequate tread depth.
Repair as necessary.
Ensure that all of the tires are inflated to the correct pressure. Refer to Tire Inflation Pressure Specifications in Maintenance and Lubrication.
Does the vehicle still exhibit poor directional stability?
Go to Step 4
System OK
4
Inspect the stabilizer shaft, links, and insulators for wear or damage.
Replace as necessary. Refer to the following:
Stabilizer Shaft Replacement in Front Suspension
Stabilizer Shaft Link Replacement in Front Suspension
Stabilizer Shaft Insulator Replacement in Front Suspension
Does the vehicle still exhibit poor directional stability?
Go to Step 5
System OK
5
Inspect the lower control arms, ball joints and tie rods for wear or damage.
Repair as necessary. Refer to the following:
Lower Control Arm Replacement in Front Suspension
Lower Ball Joint Replacement in Front Suspension
Tie Rod End Replacement - Outer in Power Steering System
Does the vehicle still exhibit poor directional stability?
Go to Step 6
System OK
6
Inspect the wheel bearings/hubs for looseness or excessive lateral runout. Refer to Wheel Bearings Diagnosis .
Does the vehicle still exhibit poor directional stability?
Go to Step 7
System OK
7
Inspect the vehicle trim height. Refer to Trim Height Inspection Procedure .
Repair as necessary.
Does the vehicle still exhibit poor directional stability?
Go to Step 8
System OK
8
Inspect and adjust the wheel alignment as necessary. Refer to Measuring Wheel Alignment in Wheel Alignment.
Does the vehicle still exhibit poor directional stability?
Go to Step 9
System OK
9
Inspect the steering gear and steering column for looseness. Refer to Power Steering System Test Procedure in Power Steering System.
Repair as necessary.
Did you complete the repair?
Go to Step 10
--
10
Operate the vehicle in order to verify the repair.
Did you correct the condition?
System OK
Go to Step 3
Vehicle Leads/Pulls
Step
Action
Yes
No
DEFINITION: At a constant highway speed on a typical straight road, lead/pull is the amount of effort required at the steering wheel to maintain the vehicle's straight path.
1
Did you review the General Description and perform the visual/physical inspections?
Go to Step 2
Go to Symptoms - Suspension General Diagnosis
2
Road test the vehicle in order to verify the complaint.
Does the vehicle operate normally?
System OK
Go to Step 3
3
Inspect the tire/wheel assemblies for:
Correct tire pressure--Refer to the tire placard.
Correct tire size--Refer to the tire placard.
Abnormal tire wear or damage
Did you find and correct the condition?
Go to Step 9
Go to Step 4
4
Perform the Radial Tire Lead/Pull Correction in Tires and Wheels.
Did you find and correct the condition?
Go to Step 9
Go to Step 5
5
Inspect and correct/adjust the suspension and steering systems for:
Vehicle trim height--Refer to Trim Height Specifications .
Excessively worn, loose, or damaged components
Did you find and correct the condition?
Go to Step 9
Go to Step 6
6
Inspect the brake system for brake drag. With the vehicle suspended on a hoist, brake drag can be identified by rotating each wheel several times and observing whether more force is need to rotate the left wheel or the right wheel. Refer to Diagnostic Starting Point - Disc Brakes in Disc Brakes.
Did you find and correct the condition?
Go to Step 9
Go to Step 7
7
Inspect the wheel alignment and adjust as necessary. Refer to Measuring Wheel Alignment in Wheel Alignment.
Did you correct the condition?
Go to Step 9
Go to Step 8
8
Inspect the steering gear for unequal effort. The vehicle must be suspended on a hoist, the engine running, and the transmission in park or neutral. Grasp the tire assembly and manually simulate a turn from the left of center and the right of center observing whether more force is needed to turn to the left or to the right. If this condition exists replace the steering gear.
Did you correct the condition?
System OK
Go to Step 3
9
Operate the vehicle in order to verify the repair.
Did you correct the condition?
System OK
Go to Step 3