bluehatch 87

Hi my mother's truck has a issue with the transmission. One day it just stopped doing anything in gear and you can move the selector but when in gear it don't move forward or backward and the fluid is full and don't smell burnt. I figured it would of started slipping before just going out completely. Also what transmission is compatible with her truck. It's a Silverado 4x4 crew cab I believe it's the 5.3. The truck code is k10753. Any help will be greatly appreciated.