Trouble with Bulk Out transfer using Cypress CY7C64613 & uv2

I am developing a device that must send out data through the FIFO at speeds up to 4 Mbit/s. I have implemented a bulk transfer as follows:

void TD_Poll(void)                     // Called repeatedly while the device is idle
{
   if(OutOutPtr - OutInPtr > 64 | OutOutPtr < OutInPtr)
   {
      if(!(OUT2CS & 0x20))
      {
         if(OUT2BC && DMAOK)
         {
            DMAOK = FALSE;
            OUTC = OUT2BC;
            DMALEN = OUT2BC;
            DMASRC = &OUT2BUF;
            DMADEST = &OutBuffer[OutInPtr];
            DMAGO = 1;
            DMAOK = TRUE;
            OutInPtr += OUT2BC;
            if (OutInPtr >= 1024) OutInPtr = 0;
            OUT2BC = 0;
         }
      }
   }
}

In the AOUT FIFO programmable interrupt there is a similar section of code that DMA's from the OutBuffer to the A FIFO.
This code works well, but only up to 74kByte/s. Beyond that it begins skipping chunks of data. I have tried moving to an interrupt-driven design, where I place similar code in the ISR_Ep2out section but the data becomes corrupted and the interrupt does not reset. Any clues on how to remedy this would be greatly appreciated. Thanks

Jonathan Pribble