Hello all, 

I have a 2005 Chevy Impala LS 3.8L V6 automatic transmission as my daily driver work car. It has 213,xxx miles. I’ve owned it since 82k miles. Has no engine codes.

Last Saturday it started shaking/vibrating intermittently at higher speeds (55mph and up). When I say intermittently I mean it varies by trip. Some trips is sakes and vibrates. Some trips it smiths out at higher speeds. It’s continuing to worsen however.

I took it to my local shop and I explained that it had newer shocks/struts all around (December 2019). New front sway bar (2019). New pads and rotors (June 2021). Alignment (January 2020) after suspension refresh. The shop I took it to stated all tires were badly out of balance and balanced all of 4 of them. Shop also stated all from end suspension and steering components were in good condition and checked out. It drove smooth yesterday and today it’s doing the same shaking/vibrating thing on the freeway headed into work. The shaking/vibrating is mostly felt through the steering wheel and is all in the front end. I don’t feel any serious pulsating in the brake pedal. From what I’ve read online, the only other thing that could cause shaking at high speeds is spark plugs…? Last time those were changed was 135-140K miles (I don’t remember the exact number). Car does idle smoothly and gas mileage is normal so wasn’t sure that was it. Could I have gotten a bad or slightly misaligned rotor from when I did brakes a few months ago? What else can I check or troubleshoot? Thank you all for your time and expertise!