I have a D1-30 on my Bav 38 ( 2010 model year).
In neutral the engine easily revs to 3000 rpms. If I engage gear and motor forward while tied up in the marina, I can only get about 2400rpms. If the boat is in calm conditions and at sea, at full revs it easily gets to 2800rpms.
The size of prop you have may be limiting your speed. I have a 3 blade folding prop.
Otherwise, the limit on speed may be a fuel issue. Are you seeing black smoke come from the exhaust?
Craig
"Shirley Valentine"
Gold Coast
Australia