If the gearbox feels ok in use, ie not fighting you in every gear change, or not wanting to go in the next gear esp when changing down, if having to deliberately do a slow change so as not to catch the box out gear change wise, it would be likely down to the synchros.
The use of gear oil in this case can help, it is no where near as slippery as atf(TQ-D) and so helps the synchros by slowing the gears down inside the box due to more friction, the synchros in every box actually use friction to do their job!!
tabetha