Too much Fuel

I've been battling a very exasperating problem with my 2003 Grand
Caravan. It has 147,000 miles and I've never had one problem with it until
last week. It began to act as though it would stall and then not respond
when I pushed the accelerator. It also blew black smoke, and after
researching, it appeared that it may have been the fuel pressure regulator. I
went ahead and replaced the fuel pump (regulator is part of that module)
and the fuel filter.  In an attempt to keep this brief, let me just say that since
the repair sometimes it runs perfectly for many miles, and then sometimes
out of nowhere it will run too rich, blow black exhaust and not go more than
20 mph. There are no codes showing a bad fuel injector, faulty sensor, etc.
There is no pattern of evidence indicating when it will run properly and when
it won't. Yesterday, I drove it 80 miles in the morning, and it ran well. Then in
the afternoon, it was getting too much fuel, blowing black exhaust, and
wouldn't get over 20 mph. Today, it did the same thing--fine in the morning
and poor in the evening. Any help would be greatly appreciated.