Scotty,
My 2004 Volvo S80 2.5 turbo AWD has an automatic transmission and the mileage is 168K. Recently, it started bucking when I got the car above 60 or 65 mph. (It would stop bucking if I eased off the gas a bit). I took it to my mechanic, who specializes in Volvos. The problem ended after he put something called "Shudder" into the transmission fluid. I never got a good explanation from him about what caused the problem (he's a great mechanic, but not necessarily a great communicator).
What was going wrong with my transmission? Is there anything else I should do to ensure the problem doesn't happen again?
Most likely the torque converter was locking up. That is primarily what that additive is used for.
What your mechanic added to the trans is maybe a temporary fix. The shudder is a famous symptom of a bad torque converter. Needs a new one.
