[Gromit]

Sorry I can't think of a logical reason for that condition; I am definitely not the best one on this site to be asking about transmission linkage; must be thousands of other members here who can visualize the entire assembly in their sleep..

Well, maybe this will spark something - here is a photo of the linkage I saved taken by another member on this forum; you can see the factory version of that bushing I mentioned next to the cotter pin in the photo - this bushing looks different than the Dorman Help! nylon version.. probably better to get the factory one if possible.

If you don't think it is a bushing - the only other thought I can offer is (if it has been a while since you changed your transmission fluid) you could pull the transmission pan off and since you can see the operation of the "rooster comb" shift control inside the trans with the pan off and with someone in the cab operating the shift lever while you watch that part ratcheting from under the truck - you could at least rule out that your problem is in the trans part of the shifter itself. You would just look to verify that each detent on the rooster comb is engagable on its stop.