2002 2500HD keyless entry remote programming

After replacing the heater core in my 2002 chevrolet truck and having both batteries unhooked for 3 days, the remotes do not work nor does the auto door lock when you put the truck in drive and park but the locks will work from the button on the door.
Is this a lost memory problem that can be corrected by reprogramming and if so, how? Can it be done without a scanner?

Close all the vehicle doors.
Insert the ignition key into the ignition lock cylinder.
Press and hold the door unlock switch.
While holding the door lock switch in the unlock position, cycle the ignition ON, OFF, ON, OFF.
Release the door unlock switch. The doors will lock and unlock to confirm the program mode.
Press and hold the LOCK button and the UNLOCK button simultaneously on one transmitter. After a delay of approximately 15 seconds, the doors will lock and unlock to confirm the programming of that transmitter.
Repeat the previous step to program up to four transmitters.
Turn the ignition switch to the RUN position in order to exit the keyless entry transmitter mode.
Operate the transmitter functions in order to verify correct system operation.