Dakota running rough

I'm having a problem with a 98' dakota 3.9L with 145K. The truck runs fine when it first starts up. Whenever it get warmed up it starts
running rough. It seems that it idles to low also at about 650 RPM. Somtimes when you hit the gas just a little and let off the RPM's jump up to 2500 RPM and stay there for about 3 seconds. Heres whats been done. New plugs, plug wires, Distb. Cap, coil, rotor button, new Idle air control, TPS. Still runs rough and low RPM at idle. Some say that the problem with the RPM jumping high is too much fuel PSI. Also some say the computer may be bad. Anyone have any clue about it?
Thanks in advance, Scott
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