Sudden burst of power?

I've noticed lately that when I drive my moms 95 V6 5spd, it will suddenly get a kick of power. My foot will have the same amount of pressure on the acclerator, then all the sudden I will feel it accelerate. This seems to happen in 4th and 5th, though she says she feels it in 1st and 2nd. Anyone have any ideas on what it may be?

those are the secondary butterfly valves opening in the lower intake manifold.