engine missfiring and lack of power,???
 

Need some help here, My meanager has a new toy, 1990 k5 blazer,350 fuel injection. Numerous issues over past 2 months, transfer case replaced. Seal between transfer and transmission replaced.New fuel filter,new spark plugs,new battery, new cap and rotor, did not replace plug wires yet. Recently heater core went, not replaced yet bypassing it, Replaced water pump. Now having strange problem. Replaced the egr vac syl. because engine was loping. It fixed the problem then few days later the truck died on him.Would not start, towed to shop, they replaced the starter and coil. I have checked the coil and all wires with volt meter all seems to be okay, I have checked cap and rotor, looks to be okaywith exception of top of cap where coil wire plugs in seems odd compared to others. Inside of coil wire to cap seems more worn than should be. next checked egr vac syl seems okay,replaced control module, not the problem. Checked for vac leaks, dont appear to be any? I have tried just about everything I can think of, What else should I look for? I haven't used timing light yet , should I? I just dont know where to look next. I am not familiar with chevys and this one is driving me crazy..... Help ,,, any suggestions would be greatly appreciated. I am tired of being moms taxi service and he's not getting his hands on my jeep...