How do I stream from USRP receiver to transmitter in simulink without packet loss

I'm trying to stream from the input to output of an ettus X310 in Simulink. The block diagram has just 3 blocks, SDRu receiver, buffer, & SDRu Transmitter. The decimation (&interpolation) value is 200 points so the sampling rate is only 1 MHz. I maxed the frame length in the receiver to 375000. The buffer size is 2*375000. I maxed the FastSendDatagramThreshold value to 1500 in the windows registry. It's a 1 gbit Ethernet connection and a fast PC. Even at 1 MHz I'm getting a lot of underflows (I assume from the transmitter) and loss of data. I have dreams of going all the way to 200 MHz (with some simple signal processing in between.) That may be a pipe dream. Suggestions?? How do I get the throughput up?

[Ethem]

Did you try "Rapid Accelerator" mode for Simulink?