ChopperSimulation -- work in progress -- not yet working

This is a simulation approximating something I built. In an effort to troubleshoot a problem I have with the actual device (the MOSFETs quickly overheating), I put together this simulation. The simulation problem: unlike the real circuit, this one does not oscillate. I am posting this in the hopes that someone could offer advice. A few observations: 1. the real circuit uses SCT50N120 MOSFETs. I am not sure that the models, even with the added diode, resistor, and capacitor, model the actual device closely enough. 2., the inverter gates are in lieu of the real-world MAXIM MAX4429 MOSFET drivers. 3. The CMOS gate models seem to be limited to a 10 V output, when 15 V is being used in the actual device. If someone has any insight as to how I could make this simulation work, please let me know. Thank you.