GMC Repair: 1994 GMC Performance, egr system, pressure regulator

Question
I have a 1994 GMC serira with 350 motor approx. 200,000 miles. The problem I am having is after the motor runs a while it seems to run sluggish at 50 to 60 mph. Also at same speed when I let off the gas seems like the transmission starts jerking. When I come to a stop the motor acts like it wants to die, loosing the idle and then will jump back to regular idle.  Have replaced plugs and wires,and ignition module. any idea's?

Answer
It could be fuel related as to pump PRESSURE or VOLUME. Could be a faulty fuel pump pressure regulator. Could be a carbo buildup within the EGR system. There are just so many could be's that it is going to take numerous diagnostic procedures to test all the possibilities and the use of a scanner to see what all the sensors are doing.