2001 GP GT engine runs very bad

Please give me some advice, I really need some. three weeks ago my 2001 Grand Prix started running poorly under load. ON the highway it felt like it had a sock stuck in the intake, laggy, poor performance under load. Felt okay taking off from a stop. After replacing the plugs and fuel filter and having it checked by a local mechanic, he said it was the transmission, and the pontiac dealer, they said it was a clogged catalytic converter, it will now only start when the gas pedal is depressed at least halfway. I removed the catalytic converter, no effect. Also I have measured the fuel pressure at the rail it reads 60 psi, and I have also measured the cylinder compression, they all read around 200 psi. Spark is good,valve timing is good, compression is fine, plenty of fuel pressure, but still barely runs at all. What should I be looking for on this motor. Its a 3.8 L non super charged. 110,000 miles, great runnning car until this point, no problems at all !! What do you guys think the problem is?? Also.... no error codes at all when it is scanned. and the plugs are really black and lots of black smoke comes out the exhaust when I can get it running.. Help !!!!!!

Hopefully Rich, Bob, or GTPDad can help on this one. I experienced the same problem years ago but on an older GM (Oldsmobubble) car. The Manifold Absolute Pressure (MAP) sensor was the cause. As I remember, the MAP sensor monitors intake manifold vacuum which translates to engine load.

fuel pressure is 60psi? Although i am not sure what the specs are, but i believe 60 is a bit high especially for a non supercharged 3800. Does the eshaust smell rich? Could the return line be restricted or fuel pressure regulator be stuck?

As for the MAP sensor suggestion. you can unplug it and run it and see if the problem is any better. If it is, your MAP is bad.

just checked my sources, fuel pressure should be 48-55psi on a 2001 grand prix gt. 60 may be ok, but is a bit high.

Disconnect the MAF (mass air flow) sensor located on the throttle body. With engine off remove the electrical connector and start up then test driveability.

If your fuel pressure gauge is accurate fuel pressure is on the high side but not that high but I would not rule it out as the cause. Is that reading with vacuum connected or disconnected at the fuel pressure regulator? If above doesn't work then check into a possible bad fuel injector(s) since fuel injection sounds rich. Fuel pressure regulator is another possibility.

Yeah, I notice my 2000 GP SE V6 3.1L 3400 engine shut off while driving. I notice several times it happens. Could it be the different type of gasoline I put it in? Or could it be P04889-Vent solenoid control circuit malfunction?Which I received from a local mechanic code reader. Please help

Since you removed the cat, I would say that Bob's on the mark with the MAF sensor. When they fail, they will cause all kinds of wierd issues but still not trip a CEL. The fact that it's running rich suggests the air/fuel ratio is off and the MAF is one of the sensors that helps control it. Again, as Bob said, your fuel pressure reading is a little high, but if you factor in a 5-10% guage inaccuracy factor, it's close. Also, you didn't mention how old your plug wires are and what brand plugs you installed. It may be as simple as needing wires and/or good plugs.