Will not start after it gets hot.

The car will not start after it is driven and has gotten hot. It has to cool down for several hours. It will crank, but it is not getting any fire. I have replaced the MAF sensor, throttle position sensor and the idle air control motor within the last 5 years. Recently, I replaced the starter, solenoid, cables and battery. I have also replaced the ECU with a rebuilt unit. Every time I change out something, the problem seems to go away and then the car leaves me stranded somewhere. We will go back to tow it home the next day and it will fire right up. It also idles very rough and RPMs fluctuate, dropping almost to a stall before picking back up. There is also a lag in throttle response when accelerating from a stop. This car has the A4LD overdrive automatic and the dual ignition with two coil packs. It is not a California spec. vehicle, if that matters?

Thanks,
Tom