My (new to me) 2007 225 Optimaxs (only 250 hours) are hard to shift but when I unhooked the shift cable from the motor all was smooth.
Next step? Any recommendations?

You are on the right path shift cables removed at motors and they shift fine, next remove shift cables from controls and see if cables are sliding smoothly. If yes, the controller is in need of attention or replacement. If not the cables are in need of replacement. Good luck. Also check the routing of cables to make sure the bends are smooth and not too tight of a radius. Some cables are designed for tighter bends. Some are for 4” and some are 8”.

This turned out to be the nylon washer/bushing (on both engines). Replaced and smooth as silk now.