1997 Chevrolet Suburban

Engine Mechanical problem
1997 Chevy Suburban V8 Four Wheel Drive Automatic 104000 miles

I have a 1997 suburban 1500 4x4 with a 5.7 v8. A few monthes ago the engine started to start hard and run rough. After several trips the the garage and advice from some friends I have replaced several parts. It is better but still not running correctly. It did have a small fuel leak in a line so all the fuel lines from the tank to the engine were replaced. I put in a injector (spider) pump. The fuel pressure is about 60psi. This was the up graded convertion one. My voltage was a little low so I also replaced the alternator. It is now reading about 13 volts after for a while. The battery is only a few months old. The rough running starts at around 1400 rpm and is at its worst at 1700 rpm and goes away at 2100 rpm. If I keep it over 2100 it runs great. There is a little over 100000 miles on the truck and engine. Any help any one can give me would be great.
June 17, 2010.

Inspect and test all the following listed below: Oxygen sensor.
Catalytic converter.
Fuel injectors dirty/sticking.
Mass airflow sensor/Airflow meter.
Throttle position sensor.
Manifold absolute pressure sensor.
EGR Valve
Fuel pressure regulator leaking or defective fuel pump.
False air leakage.
Fuel contamination.
Foul/defective spark plugs.
Open spark plug wires.
Ignition coil/Coil packs defective.
Incorrect ignition timing.
Cap and rotor.

Note: If it doesn't apply disregard

Jun 17, 2010.