can you help me diganose the problem on 1995 Chevrolet Blazer

1995 blazer wont start turn starter over and it stay running when key is off also when started idles good but go down the road it starts to miss have brand new starter an fuelpump and alternator and sometimes i look at volt guauge its under 12

Asked by for the 1995 Chevrolet Blazer
If your Blazer continues to run with the key in the off position then your ignition lock cylinder needs replacement and when running it could be intermittently cutting the ignition off and causing the missing. My book shows 2 hours to replace the ignition lock cylinder plus parts
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alt is not putting out right shood be 14to 14.5