Welcome to our forum, Acanaceous , -
Do you have any power mods?
Have you slammed the transmission lately?
I have no idea of what may be ailing your transmission.
However, I will ring up our MT expert @
Ultramaroon for you, to see if he has any ideas.
I think it's a good plan to have the shop take a look at it, check the fluid level and maybe even change the transmission oil.
humfrz