Mazda BT-50: Automatic transmission flaring

I have a problem with the automatic transmission in my 2014 Mazda BT-50 XTR dual-cab. In one particular location I regularly visit it involves driving downhill over approx. six speed bumps. The speed when negotiating each speed bump is a cautious 5 km/h max. At the bottom of the hill I have sometimes stopped the vehicle by selecting Park or on other occasions remained in Drive. My problem is on take off to go back up the road the engine revs as if it was in Neutral, although it's in Drive and barely crawling off the mark. The vehicle will slowly creep forward until finally engaging into Drive with a loud clunking noise. Mazda has replaced the transmission solenoid harness twice and this has still not rectified the problem. Anyone else have a similar experience?