1990 YJ 2.5 4 Cylinder: Bad idle, back fire, lean, rich, missing, wont stay cranked

Hey guys I am having a huge problem with my jeep. This is the first jeep I have owned so I am kinda in the dark about them. My problems I am having is after a year a driving without any problems all the sudden it died while going about 40 MPH then it cranked right up after that it start back firing really bad couldn't get up enough RPM's to get out of first gear had to be towed home. Since the problem started I have changed a few things that I have read on this forum but it seems like every time I change something a new problem pops up. The list of things I have changed is spark Plugs, O2 sensor, TPS, injector and crankshaft postition sensor. I took apart the fuel pressure regulator and checked it and it seemed fine no cracks or damage. Since I have done all this things seems to be getting worse. Now 2 of my plugs are very lean and the other 2 are pretty rich. Not sure how that happens. The only other sensor I know that control fuel/air mixture is the MAP sensor should that be a option? or at this point is it mechanical and not electrical?..please help me out here I am running out of options before I have to pay someone to fix it. Thanks in advance