Sounds like you need a trans flush the cleaner you get it the better it will do. I know it scares you to think of a transmission rebuid but I really think a flush will help. You may even be low on fluid right now. Get a new filter and complete flush.
Also it will cost about 100 bucks to have a shop do it. Maybe a bit more.
Thinking about it, may I ask if you notice slipping in the gears or going into overdrive?
Risky depends on wether its been done it when it has needed it before. if you have 200000 miles on it and never had a change I would be scared but around 120000 and there has been a change before I wouldnt worry about it.
Mechanic
Mechanic at school corp bus garage! Experience in fleet diesel and regular automotive.