1993 Cadillac Deville Have no clue

Okay, I have a 1993 cadillac sedan deville, 4.9L with fuel port injection. I have had minor problems, but I cannot seem to find out what is going on. The car has been running very rich, found out the fuel pressure regulator was out, so it was replaced. Now, the engine sputters, and when I put it in gear to drive, the engine stalls, and does not want to accelerate. At that point, it sounds like the engine is misfiring. I have also changed the distributor cap, the spark plugs, and the fuel injector o rings. As well as new plug wires.

I was looking into it, and it appears that there is some type of knock when I try to accelerate and the car is in gear. I assume that has to do with the firing of the cylinders. And I still have some type of vacuum leak near the egr vavle. There is a loud hiss, an evident sign of a vacuum leak. What would cause a vacuum leak in that area? Could it still be the injectors? And would that cause the misfire, knock, and lack of engine power. Plus, the car is consuming a lot of fuel, I am only getting three miles to the gallon

I have checked all of the normal vacuum lines etc, and none are leaking or having problems. However, the vacuum leak is near the egr valve