99 that I sold last year with 160k on it had some slop and the tow light acted funny too. pulled steering colum cover off and pushed back the boot at the base of the shifter, found the bolt through the shift lever was loose/ tighten easy. and also the wire for the tow switch was broken at same spot. repaired both.

 

My vote is cable also. The cable is the only tie to the shifter. Adjust it tight, if its sloppy there is slop in the the adjustment ends of it. Detents in the transmission shifter set the location and the cable needs to be tight to it. The NSS is also adjustable to get the lights right.

 

Mine has started doing this as well. Manually shifting from D to 3 is not so clear since the cluster doesnt seem to follow the lever and the trans doesnt care about either. I noticed this after my engine swap, but didnt touch anything trans related during the whole process.