Car operates rough when it reaches speed of 55 + then smooths out.

From what you say she says, it sounds like the transmission fluid's low. Get her to check it in PARK, with the engine running, fully warm. Better yet if you can check it and drive the car yourself. Try to determine if the transmission's slipping or if it's an engine miss or what she's really trying to tell you. Check the automatic transmisson fluid, should be clean, clear and up to level on the transmisson dipstick. If the fluid's OK, and the transmission is acting up, there may be transmission valve body problems rather than a transmission overhaul situation. Valve body work is cheaper than an overhaul. If the fluid's black and burned smelling, the transmissionn's probably used up and needs and overhaul.