GMC Repair: Reprogram auto door locks 99 GMC Yukon, gmc yukon, gm service

Question
Hello,
I just purchased a 99 GMC Yukon LS with 70K mi 5.7L engine, old body style. I received only one key & a fob. I nearly locked both in the vehicle when I went to warm it up before work. (18 degrees here that night) I didn't get in, just reached around the steering wheel, started it and nearly closed the door when I heard "CLICK" and all the doors locked.  The way it's programmed, just turning the key to the on position locks all the doors with a five second delay, turning it to off unlocks all doors. I'd like to program it to lock at about 15mph. I live in a podunk town 120 miles from anywhere & neither of the two car dealerships here have the blanks to make a copy of this key. One says it's a passlock, the other says no. I don't know if either place knows what they're talking about.
They also didn't know if there was a way to reprogram the locking order. I've read a lot on bulletin boards in the last two days & it appears that there is a way to reprogram the locks for nearly every year but 1999. I tried a few & they didn't work. Any suggestions?
Thanks,
Kim
kims75@hotmail.com

Answer
Hi
I've got to attemp to find an Owners Manual for this vehicle. I could not find anything in GM Service about how to change the locks...There IS a way, though I do know that for sure I remember doing this a few times.
As for the key, it IS a passlock system, HOWEVER the sensor is in the SWITCH and NOT the key. So it takes a regular double side 10 cut GM key blank, should be able to get that at ANY place (hardware store etc..anywhere that makes keys in area).
Please do a follow post back, and click the "private" box... that way it wont purge.
I hope this halfway helps.
Will waiting for follow post
Pawl