Nissan Repair: engine, mercury villager, fuel pressure

Question
93 mercury villager After van warms up or runs about 1/2 hour runs rough, backfires ,cant go over 25mph.Let car sit for 20 min. runs fine for another 1/2 hr same problem. Had at repair shop replaced fuel pump said it was losing pressure.Still have the same problem . Ive replaced entire exhaust including converter thinking maybe it was blocked.Possible causes ignition module or some other sensor?

Answer
Mark,

It could be the distributor or something ignition related.  Backfire is the key here.  There is something causing the car to fire when it is not supposed to.  Loosing fuel pressure would cause the engine to die but not backfire.  I would be looking at the ignition and the possibility of a defective distributor.