Sudden RPM Loss

The PIP is the first place to look. When it starts to fail, it can cause no-starts when the engine is warm. Essentially, the PIP is an essential part of the ignition system, transferring electrical power to each of the cylinders. When it starts to fail, it can do some really weird stuff. You've replaced just about everything else that could be a problem, so replacing the PIP is next.

Of course, to replace it you need to disassemble the distributor. There's a how-to buried somewhere in this forum, do some searches and I'm sure you'll find it. If you decide to replace the distributor, be careful with remanufactured ones. Most of the time, they don't replace the PIP. They test them when the parts are cold, and a bad PIP will test OK when cold.