still stutters and sometimes backfires

OK, I`m still having problems with a stutter at a certain postion in the gas pedal and it will backfire if kept there. Before it would happen when above 45 and cruising on the highway. Now It will do it at 35 and above. It is ok when accellerating. I have now replaced the following: TPS, CPS, O2 sensor, MAP, MAT, EGR valve and gasket, CCV hose assembly, cleaned the throttle body (new gasket), cleaned the inside of the valvecover(needed new gasket), serpentine belt, plugs and wires (hope I remembered all of it). I still have some oil blow-by after cleaning the vavlecover so well you eat off of it and replacing the CCV hoses. Any other suggestions?
88 4.0L auto 126K miles

There is a TSB for a bucking or suging condition. Recommends reindexing the distirbutor. usually for a fairly new vehicle or one with a new cam.
A vacuum test at the intake should tell you something. If the needle wags radiacally, somethings serious wrong.
I´d double check to make sure all the plug cables are seated all the way onto the electrodes at the plugs and cap.
Jneary had some advice on TPS adjustment, that worked for me.
Double check the wiring for the O2 sensor, knock sesnor and the temp. sender for the computer. It has a nasty habit of flopping onto the exhaust manifold and/or rubbing on the front of the motor, before it joins the injector rail harness.
Possible you have a resistance problem in a connector, between the O2 sensor and the ECU.
Word to the wise, don´t unplug the C101 connector. It´s easier to unplug the ECU and check for resitance from there. Gonna need a good wiring diagram, if you start torubleshooting the harness.

Where would I hook into for the vacuum test??? I just got a vacuum gauge.

You can put a "T" in the major vacuum line at the back of the intake or you can disconnect the vacuum line going to the back top of the air box (for the heat door in the airbox), that comes from the vacuum tree at the front of the intake. The closer you get to the intake manifold itself, the better (more accurate) the reading. The plastic lines hooked to the vacuum tree are brittle, be careful, I usually pry the end at the tree a little, with a screw driver to loosen the rubber connector a bit and twist a little, before I try removing a line.

Thanks 8MUD I will try that.

I had a stumbling/studdering problem at one time (annoyed the hell out of me). A cheap thing to try is to go to your local pep boys at the (red rose commons or lincoln highway) and get the big can of carb and choke cleaner. one at a time pull every vacuum line coming out from the intake manifold and spray into each hole. I see that you replaced the mat sensor on the intake manifold. If I can remember, there are like two of them, one next to the mat sensor and the other has the lines going the the fuel pressure regulator and to the gang vacuum connection. I also sprayed into where the map sensor rubber connector goes into the side of the throttle body. I had the stumbling problem and replaced most of fuel system (pump, filter, and pressure regulator) which didn't fix the problem and did literally you have listed. Give it a shot, my vacuum holes were gummed (4.0 - 204,800 mi) and it was stumbling til I did these this cleaning.
BTW when and if you do take my advice, be nice to the starter when cranking, it WILL take several long ones to turn over and burn off the carb spray.