so what do the clutch plates do?
OP described that car rolls backwards on hills in drive, that sounded like torque converter to me -- not sending through the same amount of torque that it used to at idle
The hard part about a post like this is that it's very subjective and without being there to look at and drive the car there is no way to know if there's actually an issue or not. I've driven lots of automatics that can roll backward a bit on an incline when the engine is idling.
There are a several sets of clutches in an automatic transmission and they are applied and released using hydraulic pressure during upshifts and downshifts. When a car is stationary the first gear clutch will be applied but the car can remain stationary because there is no direct mechanical connection between the engine and transmission.
The torque converter clutch typically only engages at cruising speeds. In fact, if you're cruising at a steady 65 mph and tap the gas just enough to see the tach raise just a few hundred RPM it's probably the torque converter clutch disengaging. Anything more and the transmission will probably downshift.