One problem related to ignition switch has been reported for the 1999 GMC Jimmy. The most recently reported issues are listed below.
Starting from January 13, 2007 ,everytime I turn the ignition off the key cannot be removed from the ignition switch. I have had to jiggle the key, and wait several minutes before the key can be removed. After researching this problem on the internet, I found many others are having/had this problem. Many ways to fix this problem were posted. Finally I found one that works for my truck. At least for now it does. I had to remove a plastic cap under the switch on the steering column, and insert an ink pen pushing against something to get the key to released. This needs to be recalled and fixed before someone dies because they can't remove their key so they can get out of their vehicle, in an emergency situation.