Torque converter problem

Hi, no codes are present at this time. My car up shifts constantly when driving at around forty five mph. Is this because of the five speed transmission cannot handle the speed in fifth gear? It just seem that the torque converter is also engaging and disengaging smoothly but all the time. Is this normal for this car/transmission to act this way? Could it be clogged fuel injectors making the car labor in turn making the transmission work harder? I have tried fuel injection cleaner in the tank. I did the transmission service at 25,000 miles. The fluid was clean and replaced with the updated Honda fluid. I also noticed after I changed the fluid there is an external filter could changing that help? Any help is appreciated. Thanks

Neil