Lord Mounts
Changing Lord mounts sure can effect performance, many times I have seen them installed in the wrong positions or with the wrong or missing spacers effecting the thrust line turning the plane into a dog. Get an inclinometer and check the difference between the levelling point (top of tail one behind rear window) and the pushrod tubes.
Mechanical tachos are also problematic, get it checked you may be surprised how far out they can be.