'93 Toyota Pickup. Why is my engine not accelerating as it should at certain points?

At first it feels like the idle drops to below where it should be, and almost feels like the engine will stall out. As I accelerate, it feels as if the engine isn't getting enough gas or producing enough power, and isn't accelerating at the pace that it should be, or going the speed that it should be. But when the gas pedal reaches a certain point, it will jump to the speed/acceleration it should be at. Sometimes you have to play with the clutch and gas to make sure you don't stall, but then the power jumps up.