02 Honda Accord flutters in 4th gear

I was gradually accelerating on the highway and noticed that just as I reached about 55 mph and slipped into 4th gear (auto trans-4cyl) there was a definite change in the smooth drive I am accustomed to. I could feel a slight roughness. I exited the highway and re-entered again accelerating gradually. The rough drive only starts at the instant it shifts into 4th gear. The check engine light did not come on. I checked the fluid level-it was okay. I added Heet (dry-gas)-no change noticed after one week. The problem persists. Does this sound like a transmission problem? Does the engine adjust in any way when changing gears-like a sensor that may readjust the fuel injection amounts or something similar. Any similar experiences or ideas?

 

Could simply be an ignition misfire, a sign that your in need of a tuneup. Both the higher vehicle speed and the lower engine rpm of 4th gear increase the high voltage required of the ignition system. A weak system could be starting to stumble under these conditions.