Increasing torque on transmissions causes RPM drop

I have had my Rodeo for just over a year now and have noticed that when I put a lot of torque on the transmission (accelerate hard, accelerate up a steep hill from a stop, reverse up a steep hill from a stop), my RPM's will drop to the point that if I don't let off the accelerator, the car will die. It is especially bad in reverse. I can hardly back out of a steep driveway without killing the car. It is an automatic transmission. When it drops RPMS, if I keep pushing the accelerator, eventually the RPMs will increase, but with a huge "clank" as if the tranny binded or slipped. Any thoughts? Make and model are in my signature.