Sorry for the late very late reply, do you have the correct adjustment tools to install the lower shift cable? A possible reason for the tough shifting could be your ESA switches are not adjusted properly or not working. They should shift relatively easy.
There is also the shift fork that needs...
Besides the gears what else did you replace? Do you know what caused the failure?
My thinking is could there be damage to the gearcase or a difference in another part where additional shims may be required. #51 are shims, there are different thicknesses of shims available.
Is the propeller shaft too high or the pinion shaft too low?
Is the pinion gear positioned correctly on the pinion shaft? Ie: not being drawn high enough when the nut is tightened.
