programing auto door locks

:banghead: here's the deal . my 2002 trailblazer door locks lock as soon as i start the truck. it locked me out the other day. there is instructions in the owners manual on how to reprogram this feature. but i tried it and it is not working anyone have suggestions. it seems the manual is missing the last step.

Try it again and do it word for word! Don't skip anything!

My sisters 02 LS is having this problem. I tried entering the program mode but the horn doesn't beep twice upon entering the mode. I hear the beeps when pressing the door lock switch. I turn the key to run and hear the horn beep twice. Still........ Get in truck, start truck, doors lock. Turn truck off, all doors unlock. I'm confused.