Probly need a tad more information. How far did you have to be on the highway, what do you use to shift, sound, tach, watching the speedo etc. Though I doubt shifting is the culprit. How did the bike act with more throttle. Have you suffered MPG lately … knowing you have had a time with your carburetor I would look into possible adjustments. Fuel delivery, spark timing etc can all slow you down a bit.
Really though …more information would be needed.