Used 4t65eHD transmission.  Please select the mileage you're looking for.  A core is a rebuildable transmission. It may have bad electronic components, it will most likely have worn out clutches. Most of the hardparts should be in useable condition so they can be re-installed when rebuilt. Because core transmissions may or may not be functioning transmissions, they will carry no warranty.
All the other transmissions will be fully functioning, and carry a 90-day limited warranty against defects in the trans. Failures due to abuse will not be covered. Manual shifting, neutral drops, one-wheel-burnouts, and general mis-use of the transmission would be considered abuse.