Paul,
Are you using a cat rig or sloop rig mainsail.
I agree with the above posts.
In addition to this I have done some two boat testing with sloop cut mainsails sailing in cat rigged config on my Taipan and the following is what I have found. I don't know if it applies to your situation but it may give you some things to try.
If your using a sloop rigged sail then I would look at 4 things. Downhaul, rotation ,outhaul and last where you stand when trapezing.
I have a tell tail one or two inches behind the mast half way up. I pull my rotation in far enough to get the tell tails on both sides streaming. Pull the downhaul down enough to make the middle tell tail on the leach stream in light air and enough to make the boat drive and not lift when the breese increases. (In general if you flatten your mainsail out too much you won't point.)
If this is all right have a look at your outhaul. I'd ease it 1 inch first up and see how you go. I have found that if you ease the traveller to make the boat drive rather than lift and don't ease the foot of the sail you lose your ability to point. It works great when you get the two just right. If you ease the foot too much you start to feel weather helm and go slow. The last thing to consider is where you are standing when trapping.
If you trap behind the centrecase the bows lift too much and the boat will run off too much. If you trap too far forward the boat will point but if you are so far forward that you feel weather helm you are too far forward and VMG will be slow.
These are just things to try. When you find the answer please fill us in.

I hope this helps.
Regards,
Phill