1994 Chevy Cheyenne Ignition rattle?

Engine Performance problem
1994 Chevy Cheyenne V8 Two Wheel Drive Manual 140K miles

My truck started making what seems to be an ignition rattle when under a load.
I checked the timing by disconnecting the tan & black wire like instructed, set the base timing at 0, I have replaced the TPS switch, the MAP sensor, the knock sensor, removed the dist. & Cleaned it, replaced the cap, rotor, plugs & wires. Thought maybe the fuel pump was getting weak & still have the rattling that starts at half throttle.
I also pushed on the diaphram in the EGR while engine is running, it tries to kill the engine, so I assume that its working.
Plese help me, I'm about to give up on this truck!
Thanks!