2004 Silverado clunk

When coming to a stop and letting off the brake there is a loud clunk if you will and sounds and feels like the underneath shifts forward and then letting off the brake shifts backwards. Transmission shifts smoothly and quietly.

Possible worn engine/trans mounts.

If it happens in reverse too, it’s probably a ventilation system part like a blend door or some other one. My GMC does it all the time and it doesn’t bother me one bit.

You might want to check for worn lower ball joints.