[jclark003]

I've had many cables fool me into thinking I had issues with the throttle/shift linkage or the gear linkage. If you haven't done so I would recommend disconnecting the cable and see if it actually is the shifting lever and linkage. Usually the cables pop right off after removing the end cover. A binding cable can put stress on the mechanism and make it seem like that is the problem. They can also telegraph noise to both ends. Swapping cables is an easy test as well.

Otherwise you can try a spray penetrating oil like pb blaster, then follow up with a spray lithium grease. Also some linkages have a teflon sleeve at the base to reduce friction. Compare both sides and see if one is missing or has failed.