I have done several searches trying to find any mention of shift linkage maintenance/lubrication. Moving the shifter between P, R, N & D is not as crisp as it used to be. Any thoughts/suggestions?

Could climb under the truck and check to see if the linkage is rusted, looking rough. Usually when I have my truck over the pit at work I'll give the linkages a spray with some Fluid Film, or Honey Goo.

the firm "click" or posn of the gear selection is inside the tranny its a spring loaded ball that lockes each gear selection, I suspose the "rooster comb" could be worn out, you would have to drop the pan and remove the VB to look at it, more than likely the linkage externally could use a little lubing, that might help, it could be so dry and tight that you have to slip past the "ball" to get it to lock in each gear.

if you unhook the shifter rod nfrom the tranny, then move the shifter thru its range you will have a good idea if its too dry