Create a blendspace with 1 axis for velocity. Put your stationary jump anim sequence on the left (0) and your running jump anim sequence on the right (which is set to whatever speed you want the running animation to be used). Then use that blendspace in your state machine instead of your jump animation. In your event graph for the anim blueprint, set the speed of your pawn to a variable so it use in the state to be sent to the blendspace. See screenshots, this is how I did what you are trying to do.