LTC3703 in boost mode

I am trying to use the LTC3703 in boost mode to create 24V from 12V SLA batteries.  I have copied the example circuit on page 34 of the LTC3703 datasheet and am using the suggested inductor and mosfets.  The circuit draws a lot of current (around 800mA with no load on the output) and the output doesn't reach 24V.  I have also tried it with a resistive test load on the output with the same results.  It looks as though as it ramps up, voltage drop across the 10ohm Rf resistor to the Vcc pin causes Vcc to drop too low and reset the chip.  This cycle continues repeatedly and the circuit never stabilizes.  The frequency of this cycle and the resulting average output voltage increases if I let the circuit draw more current but tops out at around 800mA and an average Vout of about 21V.  Any ideas on what might be wrong?

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