Mike Stone's C-17 Globemaster

Downloaded this aircraft, repainted it in RAAF colours, but am having a pig of a time trying to fly this thing.No disrespect to Mike, it could be something im not doing right.The problem im having is when the autopilot is trying to capture the altitude whilst climbing. When it does try to capture, it porpoises like you wouldnt believe, up to 3000ft + and -, and continues to do so, it just wont capture the selected altitude. Does anybody else have troubles similar to mine with this aircraft?