Why when i press the gas pedal on my pickup from a standstill, i lose power

[Zack Childers]

for a half second orso and thengo? im not sure about the level of the transmissions fluid, there arent any noises just an absence of noise, nothings burning though oil leaks, its an automatic, and its a 85 gmc sierra classic. the engine is a 400 small block. hope this helps