Greasing the slip yoke ONLY applies to the "dry yoke" style found in '96 models onwards which look like this, minus the tail shaft obviouslt...
The "wet yoke" style you do NOT grease as they are lubricated by the fluid inside the t/case, they look like this, again minus the tail shaft...
Just for interests sake a slip yoke eliminator or SYE looks like this when installed on a "wet yoke" t/case.
Or the strengthened version (not commercially available) looks like this, again a wet yoke t/case...
Cheers, JJ