EGR Problems

I have had a 93 Rodeo now for about 8 years and this last year has been a doozy! It is a 3.2L with 148K miles on it. I keep getting the Check Engine light on after I drive it for a while. I checked it and the code was for the EGR valve. I replaced it, the vacuum hoses that go to it, the backpressure transducer, and the O2 sensor. The Check Engine light still comes on reading the same code. The light comes on only after I drive it for a while and it stays on until the vehicle comes to idle then it come sright back on when I start driving again. It spits, sputters, black smoke pours out the back, a bad smell fills up the back of the cabin, and when all of this is going on, I can't get it to go over 35 MPH and the RPMs are sporatic. The tail pipe is loaded with carbon deposits. I took it in to a mechanic and he said that it was not the EGR valve, and that it was a switch/ sensor located near the EGR valve that works with the EGR. Could it be the catalytic converter? My uncle has a 92 Rodeo, and he was having problems that turned out to be the cat. It eats up gas and has become very unreliable on trips. Does anyone out there know what's going on?