Driveline lash or clunk which the dealer says will not affect normal operation
It’s a common problem with Silverados. Have the dealer lubricate the slip yoke. If the problem persists you may have to escalate it to GM Corporate. The number will be in your Owner’s Manual. You shouldn’t have to live with a vehicle that makes unnecessary noises. https://www.tomorrowstechnician.com/driveline-clunk-or-knock-caused-by-slip-yoke/
Slip yoke problem is my guess too and where to start. Check idle rpm is correct too.
According to safercar.gov, these manufacturer communications might deal with your issue:
20NA142: shudder/surging while driving
18NA355: replace trans fluid to correct shudder during acceleration
PIP5504C: vehicles that have fishbite, chuggle, misfire, AFM disturbances or torque converter shudder/vibration concerns
16NA019: Information on Transmission Adaptive Functions and Correcting Low Mileage Harsh Shifts, Slips, or Flares.
990420002K: This informational bulletin provides information on Driveline Clunk Noise and what is acceptable and what is considered normal operations.
17NA228: This informational bulletin provides information on Click or Tick Noise on 3-4 Shift that it should be considered a normal characteristic.
PIE0405A: This engineering informational bulletin is requesting information from the field on vehicles that have the condition of a Torque Converter Shudder.
There are a few others for transmission shifts between specific gears. You can find them at the above reference.