Grumpy_Mike:
you might need the gate-source resistors as low as 100 ohms (which would mean using 2W resistors!)
A 2W resistor to switch a 10nF capacitor, that sounds a bit excessive. It is not a continuous current rating we are working with.
But if the switching time is otherwise 100us and you're sending a 4.5kHz square wave to it, the FETs will be in linear mode the whole time again and possibly dissipating a lot more than 2W. Certainly 10k gate-pull-down is not really compatible with PWM at kHz rates
BTW all we know so far is that the FETs are getting 4.5kHz and running off 12V - have no idea what the load is, would be nice to know.
It does seem to me that a 1/2 H-bridge MOSFET driver chip is going to solve these problems (do many of them support n+p channel though?)