I have STS 3.6 20005.
From last few days i have observed increased RPM. e.g. before at 70MPH RPM 2200 but now its 2400^2500.
I also feel the drive is not that smooth, feeling like something reducing the power.
To eliminate the "slip" in the hydraulic coupling, the TC contains a set of clutches that Lock 100% when at hiway speeds (usually something like 40mph+ in high gear). That slip being eliminated can sometimes "feel" like a shift and a corresponding drop in rpm.