So the tank is refilling to the right level, and whatever water runs into the bowl stays there, but the bowl isn't filling sufficiently, correct?
I would check the refill tube to make sure it isn't kinked or squished at either end. Step one is going to be getting a little more water in there. Impatient person that I am, I might just go to Lowes and get a Korky 528MP fill valve and swap it for the one in there; it has an adjustable refill percentage so you can set it as you like. It's basically-identical to the other valve that Toto uses.
It's like $11.
http://www.lowes.com/pd_336988-868-528MPK_0__?productId=3284948
Alternatively, I would call Toto customer service and discuss it with them. They will probably send you a new fill valve for free, assuming that you can be sure that this isn't a hose problem. Friendly folks in Georgia, USA: 1-888-295-8134
It's either the hose is narrowed somewhere or the fill valve isn't delivering the proper refill percentage. Like I said, you can kluge the issue by raising the water level in the tank a little, but swapping the fill valve is another possibility.
Longer-shot possibilities include that something is causing the flush to not finish and start bowl refill at the expected time, leading to a late start to the bowl actually refilling while the tank has been filling and water running through the riser is going down the bowl with the flush rather than being used to refill it. Some of that is expected, but too much and you don't get a full refill. However, on the gmax flush, it should take place so quickly, this shouldn't really be possible.