Here is a copy of a release letter dated in February 1989 outlining the Syclone concept. Given the date and the truck description, I am certain this letter pertains to the recognized 1989 White Syclone concept picture that can be found online.

Click image for larger version  Name:	SycloneConcept1989_GMLetter.jpg Views:	1 Size:	109.5 KB ID:	864

Click image for larger version  Name:	SycloneConcept1989_GMLetter2.jpg Views:	1 Size:	87.1 KB ID:	865

Click image for larger version  Name:	1989SyPrototype.jpg Views:	1 Size:	94.9 KB ID:	866