To describe what is happening: Driving on the freeway in "3" I push the gear selector into "D' around 2700rpm. When I do so the tach climbs up to nearly 4000rpm and them slowly moves down to about 2700 as the car accelarates. It used to just drop the rpms and the car would accelarate smoothly. It seems to still accelarate smoothly now but I hear the engine rev and observe the tach climing. It looks like it's slipping but I'm still moving!?! It seems like the transmission is only partially engaging and I hear the engine reving. This is very confusing. Any thoughts on diagnosis?

Also: I know that the condition of the tranny fluid is very good; I had the tranny flushed and refilled twice in a row. The fluid is brand new.

HELP! and thank you