It will be on the ball at the very end of your shifter where it slides into the shift rail. Unbolt the shift tower from the transmission to get to it. I assume you have a lot of play in the shifter? I have not replaced one in that year transmission, but I think some of those had plastic shift towers where the housing itself could wear and cause slop. The bushings are listed on ebay by searching nv3500 shifter ball cup. It is pretty easy to pull the shift tower to determine if the bushing is the problem.