Engine revs without the transmission shifting to a higher gear

The engine revs without the transmission shifting to a higher gear until the throttle pedal is released a little and pressed again before the transmission shift. I changed the gearbox but the problem persists. It uses ABS sensor for transmission shifting, however the gearbox comes with transmission speed sensor. Could that be the problem? I noticed that when the throttle position sensor is unplugged the transmission shift though not smoothly with much fuel consumption. I changed the sensor but the problem remain. The car was scanned and the four ABS sensors read 'after' instead of zero when the vehicle was at rest.