Torque converter shudder?

I have a 2004 Acura TSX with 118,000 miles on it. It’s having a funny little thing for the past few months… It has a sort of shudder, or stutter, usually between 45 and 55 mph. My mechanic says it feels like a torque converter clutch shudder. He suggested draining the transmission fluid and adding “shudder stop”, some product you put in there. I called Acura (national number), they said definitely don’t add shudder stop. I am leery of my Acura dealer because they’ve been rude to me in the past and, I think, overcharged me. So, I hate to call them. I don’t really have a definite diagnosis. Any ideas?

And also, for a year or more the car has been losing oil, about 1 qt/3000 miles. No leak. No one has figured out where that oil is going. don’t know if it’s related to this newer problem

If your mechanic is just a general mechanic and doesn’t specialize in transmissions, then find a local, independent shop that does specialize in transmissions.

Given your description, TCC shudder sounds like a good bet. When you get a recommendation you want it from someone with specialized expertise.