96 jimmy jumping against starter

timing is fixed as far as manual adjustments go on this motor, I am having the same issue, i can tell you what it is not, cam / crank sensors, ignition control module, fuel pressure (60+psi), plugs, wires, cap, rotor, coil. mine has spark, fuel(60+ psi), rotor turns with engine cranking, checked timing - mark #6 on distributor lines up tdc compression stroke cyl 1 and balancer mark aligned with timing mark on block. i need ideas also, PCM (timing problem) DIAG ANYBODY?