A little background: This is my 5th ‘Vette, including a frame-off of a ’66 coupe.
Earlier this year, my 2015 LT2 began vibrating (the “rumble strips” mentioned in PIP5337C) very badly. I babied it back home and took it to the local Chevy dealer. After several days, they called to tell me the car was ready and the torque converter had been replaced. With subsequent driving, I noticed that the engine appeared to be misfiring. I would be driving down the road in V4 or V8 mode and the car would shudder, not as badly as before the torque converter, and the vibration appeared to be coming from the engine, as opposed to the rear end with the converter problem. The mechanic tried to convince me the shudder I was feeling was the transition between V4 and V8 modes. This is not the case as I always drive with the V4/V8 indication and I can watch it steadily, sometimes at 80mph and it is not indicating any change when I feel this shudder. I was aware from the day I bought it, new, that there was a slight resonance when the car changed from V4 to V8 or vice versa, so I am familiar with this sensation, and this is not what I am feeling now. If I drive in Manual mode, shift to 6th or 7th gear, there is no misfire. In addition, I drove the car about 10000 miles before the converter problem and the car was not shuddering/misfiring as it is now.

 

If your engine was misfiring the check engine light would be flashing. From what you are telling us the computer is showing no codes. Maybe the engine's serpentine belt system? A bad pulley or belt alignment.

 

 

A little clarification: This condition is not steady, as I would expect from a belt or pulley problem. Sometimes I may get a few miles down the road in between the shudders, sometimes a few yards. I am wondering if the new torque converter is defective. I spoke to the service manager at another dealer and he said I may have gotten one of the original, defective converters as a replacement. Anyway, thanks for your suggestion.

 

If it was intermittently missing you would see a flashing CEL. More serious problem would be a constant CEL. Good chance you would hear it as a miss in these cars sounds like marbles rolling around in a can.

 

A belt or pulley can vibrate/shutter than correct itself than vibrate/shutter again for reasons like a dry bearing right before failing. Thinking, a bad idler pulley bearing will act like this.

 

Thanks for the advice. I'm tallying all these ideas so I can have a "nice" conversation with a skeptical mechanic.

 

Another suggestion would be to check for any loose spark plug wires which has been known to happen.
Good Luck with finding the problem.

 

Thanks. Another thing I can check.
Thanks

 

I tested the car in Manual mode, by using the shifter, bumped it up to 7th or 8th gear, depending on the speed, and the car drives perfectly, albeit in V8 mode. If I don't touch the shifter, leave the shifter in Drive, but flip the UP paddle shifter, and go up to 7th or 8th gear, it will go between V4 and V8 mode, and I have the problem, even if the dash indicates that no V4/V8 transition is happening. The more I drive, it seems as if the problem I had before they replaced the torque converter is raising it's ugly head. i.e. the "rumble strips" convulsions.
Thanks for the suggestion. I have called the GM Assistance Center and they say they will get involved. Here I sit, holding my breath.