Yes, T6 is full synthetic. I'm not sure if the other Rotellas are JASO-MA certified. If they are not, that would probably be the reason for problems if used.It absolutely was an issue in some of the '13s. What Yamaha has or has not done to the clutch material since then I cannot say. And I am certainly not against using Rotella, I just remember that there was an issue so I threw it out there.I've used Rotella T6 since my second oil change and have not had any issues 45k miles later. Just wanted to let others know that this oil is not likely an issue.At the risk of getting flamed, what oil are you using? There were some early complaints that oils (Specifically Rotella) that worked just fine in Gen1 and Gen2 bikes caused difficult/sticky shifting in the Gen3.
Also, I think the T6 is the full synthetic Rotella? My Duramax currently has 2 and a half gallons of that inside it.
SouthernCruizer was one of those affected if I recall correctly.
Regardless, hopefully the OP gets this figured out!