I have 2800 mile on my 2024 c8 and it just started shaking/rum rumbling going into second and 3rd. Also if I stay in the range of 40-45 mph it'll do the same. When I switch to z mode it drives co pletely smooth and nothing is wrong. Any help would be appreciated thank you

 

It shouldn't be happening, of course, regardless of the driver mode setting. The setting that is likely affecting the appearance of the issue is the engine/shift setting. In Tour mode, that setting is defaulted to Tour and cannot be changed. In Z mode, you can change that setting. Where do you have yours set?

If that is the setting that is affecting what you observe, you should be able to verify by staying in Z driver mode, and just changing the engine/shift setting from Tour, to Sport, or to Track, and seeing if the same pattern results. That will do nothing to help with why you have the issue, other than its some issue with transmission or the software controlling it.

Those settings do change the shift points (the RPMs where the shifts will occur), and will change the gear/rpm for normal cruising (it will seek 1500 rpm or so in Tour, and 2500 or so in Sport or Track settings of engine/shift). It also changes (some report) the snappiness (clutch engagement?) of the shift - so its quicker in Sport or Track than in Tour. None of which should cause shuddering when all is working as designed.

Did you a software update recently? There are adaptive parameters in the transmission control software that allow it to adapt/adjust the clutch engagement pressures as the clutches wear, describe in the service manual. Its been reported that some transmission jerkiness is experienced after certain updates - if so - that may smooth out on its own after a while.

 

Did you follow the "break in" instructions in the OM?
Sounds like the engine is "lugging" at lower speeds. which may have been learned during break in.