Programing door locks

Can anyone tell me how to program the power door locks on a 1999
Silverado? (Lock when transmission is shifted into drive vs. lock at a certain vehicle speed-etc)

While I'm not certain how to reprogram, I am just curious as to why you would want to change it?

I would like to re-program the locks because they now automaticaly lock at about 15 mph and they don't automaticaly unlock when the transmission is shifted into park. I understand that you are not absolutely certain of the exact details of the procedure involved in re-programing the locks, however a little trial and error plus your information might be just the ticket. Thanks for your interest and help