96 Accord, clutch not always engaged

Just had Master and slave cylinders replaced do to leaks (120K miles). Now have problems.

On long-trips, +40min on highway, I feel like the car no longer has pickup as if clutch is slipping although no foot on pedal. Also on same trip, in stop and go traffic, I had no pick-up in first or second gear (lots of reving no Horsepower).

This problem does not seem to happen when just driving around town?

Fluid levels look fine (maybe a little high).

Should I have the system bled? Could it be air expanding under heat during long trips?

Any idea welcome.