I visually look at them. Look for cracks in the rubber.
Most mounts have a bolt/sleeve going horizontally through the middle.
If the rubber has a crack between the middle and outer edge, either replace it or rebuild it with polyeurethane. Mine are solid mounts that I made at my garage, and they work really good.

If the engine has a torque link (mine does), and if it is loose/cracked rubber, that will affect your shifting.

A cracked-rubber transmission mount will affect shifting, also. If you want someone to look at it, I can show you what to look for.-no charge.-Bob