A Black Day for Mayberry - S4-E7
Plot hole: There is no reason for a gold truck from Denver to Fort Knox to be going through Mayberry.
Plot hole: In the episode "Scheming Schemers" (1956 - fake Shemp episode) at the start of the episode, Moe is given the address for a plumbing job over the phone and he and Larry take off in their jeep - accidentally leaving Shemp behind. Next scene, Moe and Larry are in the house working on their plumbing job and minutes later Shemp just shows up outside in a separate vehicle. Shemp would not have known where the job is since he was left behind and never would have known the address Moe and Larry went to.