Have a GEMS ECU with a chip from Mark Adams (Tornado) installed. Mike at ECR and Mark Adams worked over the set-up, so no immobilizer issues. I sold my 97 SW with 4.6 this was in, so no further need for it. $400 shipped CONUS.
If you need more information on this set-up, search the various threads on this forum or see www.tornadosystems.com