Are you confusing gravity assists (unpowered) with the Oberth maneuver (powered)? You can't use a gravity assist with the Sun because it's at rest relative to

Are you confusing gravity assists (unpowered) with the Oberth maneuver (powered)? You can't use a gravity assist with the Sun because it's at rest relative to the rest of the Solar system. The Sun is only ever dragging you down, whereas a gravity assist maneuver drags you around the target body. (Imagine me waving my hands a lot while you read this.) You can kind of think of it like coming up from behind a planet relative to it's motion around a star, which will will accelerate you, or going in front of it, which will slow you down. For interstellar trajectories you can use stars for gravity assists, but I'm not sure that would work for escaping the Sun. There, you would want to use the Oberth maneuver, where you get into an elliptical orbit around the sun and then fire your engines at perihelion to raise your orbit to a parabolic or hyperbolic trajectory. In any case the Voyagers both used gravity assists around the gas giants (Voyager 2 used all four, while Voyager 1 just used Jupiter and Saturn because NASA decided to swing past Titan and didn't have enough propellant left to resume the Grand Tour course).