I have 2x VP AD41Bs and notice that although she selects gear ok the second stage of operation ie throttle is very stiff initially and makes harbour and docking manourvous very difficult any ideas?
You need to identify what's causing it. (a) throttle box on dash (b) cables or (c) something in the engine. 99% of the time it's the cables, so grease/exercise them, or replace (they're cheap). In your case, it sounds like the throttle cable - the morse lever mechanics on the dash seem ok because the first part of the travel (ie the gear select) is ok.
probably already know this, but ASAP seem to offer cables cheaper by far than any one else. just replaced all of mine and cost me a fortune, next time i'll go straight to them.
Just a thought, but are both stiff? If so it might be something else, I would disconnect the throttle cables from the engine, then check them again, if they are still stiff, then I'd discoonnect them at the control end and move them by hand, if they are still stiff, bin 'em! If ok then it's got to be the controls, simple innit'!