1986 RIVIERA MISFIRE

I have an 86 Buick Riviera. The car misfires when the engine is under load. I have replaced the crankshaft sensor, crankshaft balancer pulley,new plugs and
wires,new maf sensor,new ECM,all 3 coil packs,and oxygen sensor. Between 55 and 60 mph i loose ignition for 1 second to all of the cylinders and there are no trouble codes. can anyone help me please.I dont know what to check next thanks TOM
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