can replace a 2005 impala transmission with a 2001 impala

Check the VIN number on both cars and check the tranny code, if both are the same then you are ready to go...

Where are the vin to the transmission

there is one VIN , it is a specific digit or 2 . im pretty sure the Haynes manual decodes the VIN for you and a repair manual is sometimes valuable if you plan on working on it yourself it could save thousands, good luck P.S don't bite off more then you can chew and don't be too proud to ask most generally someone has had the same problems and figured it out