Intermittent Vibration noise between 40-70mph

[Dale267]

2021 Tahoe High Country intermittently makes vibration noise between 40-70MPH. Dealer initially said it was the torque converter now they are saying it is the transmission (slippage between 3-4 gears on a 10 speed transmission).
Anybody else experience this type of failure?

 

[Lackland]

We have a 2022 doing same thing. We got told today torque converter. Recommending trans flush