Transmission or throttle body

My mechanic dad says it's the transmission filter, the shop mechanic at the car lot I bought it from, says throttle body. Long as the car is in motion, it drives fine. Accelerates a little slower than it should, but fine. If I have to stop at a stop sign or yield to traffic, or at a red light, it takes about 4 "mississippis" to accelerate. With my the pedal all the way to the ground, it barely moves. But after it gradually begins to move, it reacts like it should with the pedal mashed down and tries to take off. Hills are worse. If I'm stopped on an inclined surface, it wont move. Like if I come to a red light on a hill, I cant accelerate up hill with shifting back and forth. Sometimes I have to wait for traffic to clear and back up or turn and find another route. If I'm parked slightly down angled, there's a chance I wont be able to reverse out of the spot. Constant shifting and pedal mashing until I can clear the car next to me. And while it's doing this, the engine isn't revving or grinding. It's sitting there, my foot all the way on the ground, not moving.