neutral safety and column shift.

DO NOT put the NSS on the shifter!!! Fix "what is there." I've heard that the inner comb / shaft can come loose, which will also affect gear selection. If that is not the case, it's either shifter adjustment, wrong shifter lever on the trans (most shifters use proprietary aftermarket shift levers) or something sloppy / worn in the shifter / cable.

Of course as with the original shifter, it could also be a bad switch, or a connector / wiring problem.