This one uses a cable, I checked for a vac hose but couldnt see one. and (as far as I understand it) a faulty controll cable/vac hose would affect the shifting but not the stall speed (which, though I dont have specific data for ths model, I would expect to be around 2000) nor would it affect the "Pulling away" performance.

This one feels like trying to pull away in second gear (in a manual IYSWIM) which, if the TC isnt "Converting" is effectivly what one is trying to do.

This is why I suspect the TC rather than the box