Synthetic in the transmission might not make that any better. That's the synchro doing it's job by blocking you out until the revs are matched.

Synchros are like little clutches. When you press the lever towards the gear, the hub & the baulk ring come together at a cone-shaped surface. If it's too slippery, then the synchro has a harder time getting the gear spinning to match the hub.

What's wrong with Honda MTF? Or even GM Synchromesh?? May as well use something that's made for synchronized transmissions.