13 Impala LTZ. Engine seems to shudder at random cruising speeds and not under a load. Runs fine up hills or under acceleration. Details on the car. 220000 miles (work car) Tune up 20000 miles ago. All 4 cam sensors and timing chains (and gears) replaced in the last 5000 miles. Car runs good otherwise and use very little oil. Shuddering started before sensors and chains replaced. Checked things like drive axles (less than 50000 on them), center axle shaft, and engine mounts. All seems good. My initial thought was engine mount. Any ideas? Quite annoying.

Guessing no codes? How does the transmission fluid look? Maybe a fuel or fuel pump issue, seen some weird stuff happen with gas issues. If you have a scanner capable of capturing live data, might record a trip and see if you can catch the data when the issue occurs.

Random speeds and not under load, would not think it likely to be a motor mount. Be sure to report back when you figure it out, will probably help someone.

Nice to see someone with one of these over 200,000, a little over 160,000 on our 2012.

Thanks 12lt. Was wondering about trans also. That's one area I lack in on routine maintenance. Only code is the normal one I've had for 50000 or so. Emissions large and small leak. Will report back when I eventually figure it out. Nicest car I've ever had as a work car. Still in excellent condition. Not ready to give her up yet

Would be sure and check your fluid. The drain and change on these transmissions is really simple. Have changed the fluid on our 2012 I think 3 times and about to change it the fourth this weekend, it has a little over 160,000 miles on it.