Re: zf6 shifting issue..think its an easy fix but not sure
I would start by pulling the shifter off from inside the cab, and then if you have to, pull the top assembly off the tranny and do some more exploring from there. A LOT less work than pulling the tranny, and you might just find something out of place that you can tackle from there.
That said, it's not unthinkable that it's the shifter itself that's about to snap, as you suspect. My wife had an '83 F-150 with that Mazda top-loader 4-speed. She's 120 soaking wet, and pretty average strength. Still managed to break the shifter clean off one day. Said it felt just as you described; kinda weak and ready to break at one moment, and the next moment it's a scene from a Jerry Lewis movie. In either case, whether it's the shifter or something more "internal", I'd bet a nickel it's the, er, spirited shifting you have to do, not using the clutch, that led to it.