One problem related to mechanical jack has been reported for the 2004 GMC Envoy. The most recently reported issues are listed below.
The bumper jack is unsafe. When jacked to its full height under a load, the jack's cork screw moves, misalign itself, from the jack's body. Therefore, you are unable to screw it back into its body due to the misalignment. In order to remove the jack, I had to drive off of it.