truck dies after accelerating like its dropping a gear and feels like the engine is about to cut out

i have a 1984 gmc 4x4 with a 305 v8 with quadrajet carb and recently out driving i would push on the gas peddle and a little bit before it would go to 3rd gear it would decelerate dramatically and feel like the engine almost cut out but would feel like the slowing down effect when you shift up on a manual to slow down.
i have all my fluids in check about to change oil and i dropped and emptied the transmission pan about 600 miles ago.
please help.