I have the same problem. Seems like the engine takes a second or two to react to the opening of the throttle in fourth or fifth gear. I am betting it's the slow opening of the secondary throttle plates? I am sure someone who knows the cause will chime in shortly. While you are waiting, you might want to add to your avatar where in the US you reside and your model Rocket. Brings in a more personal touch to your entries. More importantly, helps those in the know analyze problems to a specific model or year. If new to the site, welcome aboard!