The 3000GT/Stealth shifter assembly is notoriously loose and sloppy. Part of it is in the linkage system, part in the shifter assembly, and part is just that the gearbox itself is "sloppy". The shifter lever itself can be tweaked a little with various tricks, but that still leaves the whole assembly and linkage.
This kit includes replacement full-floating brass fittings to go at the end of the shift cables connecting to the transmission to tighten up those connections, and aluminum fittings to replace the rubber floaters that support the whole shifter assembly where it mounts to the chassis. This nets a much more stable assembly with more precise shifting.
NOTE: The stabilizer kit replaced the bushings in the stock shifter frame assembly as circled below. The other bushings included are the 2 at the other end of the shifter cables where they meet the levers going into the transmission.